,,state ,,of ,,colorado ,john ,a4 ,love1 ,governor ,,department ,,of ,,natural ,,resources ,t4 ,w4 ,ten ,eyck1 ,executive ,director ,,colorado ,,geological ,,survey ,john ,w4 ,rold1 ,state ,geologist and ,director ,a4 ,l4 ,hornbaker1 ,mineral ,deposits ,geologist ,richard ,h4 ,pearl1 ,ground ,water ,geologist ,william ,p4 ,rogers1 ,engineering ,geologist ,antoinette ,m4 ,ray1 ,secretary ,,mission ,,of ,,the ,,colorado ,,geological ,,survey ,the ,colorado ,geological ,survey was legislatively re-established in ,february #aifi to meet the geologic needs of the citizens1 governmental agencies1 and mineral industries of ,colorado4 ,this modern legislation was aimed at applying geologic knowledge toward the solution of today's and tomorrow's problems of an expanding population1 mounting environmental concern1 and the growing demand for mineral resources4 ,,specific ,,legislative ,,charges3 8,assist1 consult with1 and advise state and local governmental agencies on geologic problems40 8,promote economic development of mineral resources40 8,evaluate the physical features of ,colorado with reference to present and potential human and animal use40 8,conduct studies to develop geologic information40 8,inventory the state's mineral resources40 8,collect1 preserve and distribute geologic information40 8,determine areas of geologic hazard that could affect the safety of or economic loss to the citizens of ,colorado40 8,prepare1 publish1 and distribute geologic reports1 maps1 and bulletins40 ,,prairie ,,peak and ,,plateau ,a ,,guide ,,to ,,the ,,geology ,,of ,,colorado by ,john and ,halka ,chronic ,illustration3 ,relief image of ,colorado ,,colorado ,,geological ,,survey ,,bulletin #cb #aigb ,available from ,colorado ,geological ,survey #ahde ,sherman ,street ,denver1 ,colorado #hjbjc ,price--#b4jj ,,acknowledgments ,this guidebook was written at the request of the ,colorado ,geological ,survey to fulfill a long-felt need for a popular account of the state's geology and its relationship to ,man4 ,the authors wish to thank those of their colleagues who have assisted at various times in the preparation of this book4 ,john ,rold1 ,colorado ,state ,geologist1 and ,william ,weber1 of the ,university of ,colorado ,museum staff1 made many helpful suggestions concerning the manuscript4 ,john ,schooland1 vice president of the ,colorado ,historical ,society1 generously provided several pictures of early mining activities in ,colorado4 ,permission to reproduce drawings and paintings of fossils and reconstructions of past environments was granted by the ,american ,museum of ,natural ,history and the ,university of ,colorado ,museum4 ,drawings1 maps1 and diagrams are largely the work of ,robert ,maurer1 who also designed the cover and title page4 ,illustration3 ,tilted dark red sedimentary rocks of the ,pennsylvanian-,permian ,maroon ,formation are well exposed in the cliffs of ,maroon ,bells1 southwest of ,aspen4 7,photo courtesy ,hydraulic ,unlimited ,mfg4 ,co47 ,,contents ,page ,introduction #a ,i ,colorado's ,three ,provinces #c ,the ,prairies #h ,the ,peaks #aj ,front ,range #aa ,wet ,mountains #af ,sangre de ,cristo ,range and ,spanish ,peaks #ag ,park ,range and ,rabbit ,ears ,range #ai ,gore ,range #bj ,tenmile and ,mosquito ,ranges #ba ,sawatch ,range #bb ,elk ,mountains and ,west ,elk ,mountains #bd ,san ,juan ,mountains #be ,uinta ,mountains #bf ,the ,plateaus #bh ,,ii ,geologic ,history of ,colorado #cb ,precambrian ,era #cc ,paleozoic ,era #ch ,cambrian ,period #ci ,ordovician ,period #dj ,silurian ,period #db ,devonian ,period #db ,mississippian ,period #dc ,pennsylvanian ,period #dd ,permian ,period #dh ,mesozoic ,era #ea ,triassic ,period #ea ,jurassic ,period #eb ,cretaceous ,period #ef ,cenozoic ,era #ei ,tertiary ,period #ei ,quaternary ,period #fh ,,iii ,geology and ,man in ,colorado #gd ,gold1 ,silver1 and ,other ,metals #gg ,boulder ,county #gi ,central ,city and ,idaho ,springs #hj ,georgetown1 ,empire1 and ,silver ,plume #ha ,leadville #hb ,breckenridge #hc ,fairplay #hd ,silverton #he ,ouray #hg ,aspen #hh ,creede #hi ,cripple ,creek #ij ,climax #ia ,radium1 ,uranium1 and ,vanadium #ic ,oil1 ,natural ,gas1 and ,oil ,shale #id ,coal #if ,construction ,materials #ig ,sand1 ,gravel1 and ,clay #ig ,stone #ii ,lime and ,gypsum #aja ,gems #ajb ,water #ajc ,surface ,water #ajc ,groundwater #aje ,caves #ajf ,springs #aji ,environmental ,geology #aaa ,glossary #aad ,suggested ,reading #aai ,index #aba ,,illustrations ,page ,colorado's three geologic provinces #b ,pikes ,peak1 seen from the ,garden of the ,gods #d ,rock classification 7chart7 #e ,stratigraphic column 7chart7 #g ,jurassic rocks in ,colorado 7map7 #i ,east face of ,longs ,peak #aa ,rocky ,mountain ,national ,park 7east-west profile7 #ab ,big ,thompson ,canyon1 west of ,loveland #ac ,red ,rocks ,amphitheater1 west of ,denver #ad ,colorado ,springs area 7map and cross section7 #ae ,joint systems in ,precambrian rocks1 ,boulder ,canyon #ae ,spanish ,peaks1 southwest of ,walsenburg #ah ,hahn's ,peak1 north of ,steamboat ,springs #ai ,gore ,range from the east #bj ,aspen ,mountain geology 7map7 #bc ,mt4 ,sopris1 south of ,glenwood ,springs #bd ,ouray1 in the ,san ,juan ,mountains #be ,steamboat ,rock1 ,dinosaur ,national ,monument #bg ,grand ,hogback1 near ,rifle 7block diagram7 #bh ,mt4 ,garfield1 near ,grand ,junction #cj ,precambrian-,cambrian unconformity south of ,ouray #cd ,geologic map of ,colorado #ce ,black ,canyon of the ,gunnison ,national ,monument #cf ,precambrian-,cambrian unconformity1 ,glenwood ,canyon #ch ,cambrian fossils #ci ,ordovician fossils #da ,devonian fossils #dc ,mississippian fossils #dd ,pennsylvanian paleogeography 7map7 #de ,fountain ,formation northwest of ,denver #de ,pennsylvanian fossils #df ,contorted ,pennsylvanian rocks near ,gypsum #df ,balanced ,rock1 ,garden of the ,gods #dh ,permian reptile tracks #di ,the ,flatirons1 near ,boulder #ej ,colorado ,national ,monument #ea ,morrison ,formation1 west of ,denver #ec ,dinosaur bones1 found near ,morrison #ed ,dakota ,sandstone hogback #ef ,cretaceous fossils #eg ,wolford ,mountain1 north of ,kremmling #fj ,eohippus1 the 8,dawn ,horse0 #fa ,golden and ,south ,table ,mountain #fb ,devil's ,staircase1 near ,spanish ,peaks #fc ,green ,river oil shale1 west of ,rifle #fd ,florissant ,fossil ,beds ,national ,monument #fe ,pawnee ,buttes1 north of ,fort ,morgan #ff ,fossil mammals1 northeastern ,colorado #fg ,glacial lakes in ,rocky ,mountain ,national ,park #fh ,arapaho ,glacier1 west of ,boulder #gj ,pleistocene mastodons #gb ,great ,sand ,dunes ,national ,monument #gc ,colorado ,mineral ,belt 7map7 #gh ,sluicebox mining in early ,colorado #ha ,early-day ,leadville #hb ,gold dredge1 ,fairplay #hd ,silverton1 in the ,san ,juan ,mountains #hf ,abrams ,mountain1 south of ,ouray #hg ,creede and its mines 7map7 #hi ,cripple ,creek1 near ,pikes ,peak #ij ,climax molybdenum mine 7cross section7 #ia ,rampart ,range quarry1 near ,colorado ,springs #ih ,yule ,marble quarry1 near the town of ,marble #ii ,lyons ,sandstone quarry #ajj ,university of ,colorado ,museum #ajj ,colorado-,big ,thompson ,project 7cross section7 #ajc ,san ,luis ,valley 7cross section7 #aje ,cave of the ,winds1 near ,manitou #ajg ,mesa ,verde cave and ,indian dwellings #ajh ,glenwood ,hot ,springs #aji ,,prairie ,,peak and ,,plateau ,introduction ,gold was discovered in the bed of the ,south ,platte ,river in #aheh4 ,prospectors flocked to ,colorado as they had flocked only a few years before to ,california4 ,they worked the sands and gravels of ,cherry ,creek1 ,clear ,creek1 ,boulder ,creek1 and ,california ,gulch4 ,exhausting the placer sands of the stream bottoms1 they moved higher to mine gold-bearing veins at ,central ,city and ,blackhawk4 ,mining camps sprang into existence overnight1 each heralding some new 8strike10 each populated by a new rush of fortune seekers4 ,as lower areas were mined out1 prospectors moved yet higher--to ,breckenridge1 ,gold ,hill1 and ,empire1 ,aspen1 ,leadville1 and ,cripple ,creek4 ,silver was found as well as gold1 then iron1 and later tungsten and molybdenum4 ,the metallic ring of mining tools echoed from ,colorado's peaks4 ,fortunes were made here4 ,legends were born4 ,prospectors and miners were not1 however1 the first people interested in the rocks of ,colorado4 ,earlier1 bands of nomadic ,cheyenne and ,arapaho ,indians had searched ,colorado's hills for flint for arrowheads and brightly colored clays for warpaint4 ,cliff-dwelling ,pueblo ,indians in southwestern ,colorado sought clay for their pottery and fossil seashells for the magic of their medicine men4 ,and from farther to the southwest1 ,navajo tribesmen came to ,colorado for turquoise4 ,from clay to gold1 much of ,colorado's wealth has come from her mountains4 ,but after the rush to the mines1 as veins were mined out and placers worked over1 as values and prices changed1 her population sought the riches of the prairies3 fertile lands for agriculture1 and in the rock layers below1 black gold--vast accumulations of oil and natural gas4 ,the tablelands and plateaus west of the mountains yield their wealth1 too4 ,here are valley farms1 fed often by irrigation water1 and ranch country4 ,here is more oil1 and in some areas precious metals and uranium4 ,in recent years ,colorado's prairies1 peaks1 and plateaus have brought new meaning to all ,america3 the state now provides an attractive playground for state residents and their visitors4 ,campgrounds1 streams1 lakes1 and high trails beckon in summer2 barren slopes deep in winter snow attract the skier4 ,more and more1 those who live in ,colorado and those who visit her seek to understand these mountains and hills and prairies1 to learn of her geologic origins and her far distant past4 ,for tourist and resident1 casual visitor1 ski enthusiast1 ,sunday picnicker1 for all those who have met ,colorado and enjoyed her1 this book is written4 ,illustration3 ,topographically1 scenically1 and geologically1 ,colorado can be divided into the three provinces shown here4 ,,plateaus ,,uinta ,,mts4 ,,green ,,river ,,basin ,yampa ,river ,steamboat ,springs ,,uinta ,,basin ,white ,river ,,white ,,river ,,plateau ,,roan ,,plateau ,glenwood ,springs ,colorado ,river ,grand ,junction ,,grand ,,mesa ,gunnison ,river ,,uncompahgre ,,plateau ,dolores ,river ,,paradox ,,basin ,,mesa ,,verde ,,mountains ,,north ,,park ,,rabit ,,ears ,,range ,,park ,,range ,,middle ,,park ,,gore ,,range ,,front ,,range ,,elk ,,mts4 ,aspen ,,sawatch ,,range ,leadville ,,mosquito ,,range ,fairplay ,,south ,,park ,,west ,,elk ,,mts4 ,gunnison ,salida ,,wet ,,mts4 ,,sangre ,,de ,,cristo ,,range ,,san ,,luis ,,valley ,rio ,grande ,alamosa ,,san ,,juan ,,mts4 ,ouray ,silverton ,durango ,,mesa ,,de ,,maya ,,plains ,fort ,collins ,south ,platte ,river ,denver ,,great ,,plains ,colorado ,springs ,arkansas ,river ,,wet ,,mt4 ,,valley ,,huerfano ,,park ,la ,junta ,walsenburg ,i ,colorado's ,three ,provinces ,scenically1 ,colorado is divided into three provinces3 the ,plains or ,prairies on the east1 the ,rocky ,mountains bisecting the state from north to south1 and the ,colorado ,plateaus on the west4 ,there are a number of local variations of course1 but by and large the provinces are clearly defined4 ,these three divisions will form the basis for our discussion of the geology of ,colorado1 for the scenic differences are almost exactly paralleled1 and usually controlled1 by differences in geologic structure4 ,the ,plains rise gently from an elevation of about #ccej feet at the eastern border of the state to #ejjj feet where they meet the mountains #aej miles further west4 ,two major rivers cross the ,colorado ,plains3 the ,south ,platte ,river1 flowing northeastward from the ,denver region1 and the ,arkansas ,river1 which leaves the mountains at ,canon ,city south of ,colorado ,springs and travels eastward across the southern portion of the state4 ,tributaries of these two main river systems have etched the prairie surface1 so that much of eastern ,colorado has a gently rolling1 hilly appearance4 ,the ,mountains rise abruptly along a north-south line at about #aje west longitude4 ,they reach elevations of over #ad1jjj feet at ,pikes ,peak1 ,mount ,evans1 ,longs ,peak 7all visible from far out on the plains71 and fifty other peaks further west4 ,the ranges of the ,colorado ,rockies form rank upon rank of ridges and peaks1 roughly north-south in trend1 about #ajj miles across from east to west1 extending from the northern to the southern border of the state4 ,here1 in mountain springs and lakes1 are born the rivers of ,colorado3 the ,platte1 the ,arkansas1 the ,yampa1 the ,colorado4 ,crags and cliffs tower above tree-covered slopes1 the rocks always a dominant part of the landscape4 ,the continental divide runs through the state along the summit ridges4 ,west of the divide1 all streams flow to the ,colorado ,river and the ,pacific2 east of it1 streams flow into the ,mississippi or the ,rio ,grande1 and thence to the ,gulf of ,mexico4 ,west of the highest ranges1 the country flattens out once more into the ,plateaus1 which extend across western ,colorado1 southern ,utah1 and northern ,arizona4 ,here1 the predominant land forms are flat-topped mesas and deep canyons4 ,redrock walls shimmer in the brilliance of the western sun1 offset by deep purple shadows sometimes hiding ancient cliff dwellings4 ,fragrance of pine and juniper mingles with the pungency of sage4 ,narrow tracks lure the explorer4 ,despite the canyons1 water is scarce except along major river systems1 for this is the beginning of the desert west4 ,the scenic and geologic division of the state into three north-south strips is not everywhere clearly defined4 ,in southwestern ,colorado1 the ,san ,juan ,mountains and the complicated uplifts surrounding ,ouray and ,silverton are out of key with either mountain or plateau4 ,they are best considered part of the ,mountain ,province1 however1 although they extend it far to the west4 ,other exceptions to these divisions occur also4 ,the ,mountain ,province is interrupted by four broad high-altitude valleys3 ,north ,park1 ,middle ,park1 ,south ,park1 and the ,san ,luis ,valley4 ,the ,uinta ,mountains jut into the northwest corner of ,colorado from adjacent ,utah4 ,and the ,paradox1 ,uinta1 and ,green ,river ,basins protrude into the ,plateau ,province1 modifying its topographic character4 ,illustration3 ,pikes ,peak rises to an elevation at #ad1aaj feet4 ,composed of ,pikes ,peak ,granite1 the mountain is almost surrounded by younger sedimentary rocks1 including those of the ,garden of the ,gods1 in the foreground4 7,floyd ,walters photo7 ,before discussing the geologic nature of the three provinces1 let us review briefly two sets of geologic terms4 ,the first set has to do with the rocks themselves--,what kind of rock is that8--but serves also to tell something about the origin of the rocks4 ,the second set is concerned with time--,when was that rock formed8 ,is it older or younger than adjacent rock8 ,how does it relate1 time-wise1 to geologic events in other parts of the world8 ,these two sets of terms are presented in the charts that follow4 ,if you are unfamiliar with geologic terminology1 refer to these charts as often as you need to while you read this book1 as well as to the glossary on pages #aad-aah4 ,geologists divide rocks into three main groups1 depending on their modes of origin4 ,igneous rocks originate from molten material1 cooling deep below the surface of the earth 7intrusive igneous rocks7 or flowing out and hardening at the surface 7extrusive igneous rocks74 ,sedimentary rocks are formed from broken or dissolved bits of other rock1 washed by wind and water and deposited as layers of fragments or as chemical precipitates4 ,they often contain fossil plants or animals4 ,metamorphic rocks are pre-existing rocks 7igneous or sedimentary7 changed by heat1 pressure1 or chemical action4 ,examples of these three classes of rocks are given in the accompanying figure4 ,many varieties of all three classes occur in ,colorado4 ,class ,example ,occurrence in ,colorado ,sedimentary ,sandstone ,plains1 plateaus1 flanks of mountain areas ,shale ,conglomerate ,limestone ,igneous ,extrusive3 ,volcanic areas such as ,san ,juan ,basalt ,mountains1 ,spanish ,peaks ,intrusive3 ,pikes ,peak1 ,longs ,peak1 and most ,granite central mountain areas ,diorite ,metamorphic ,marble ,mountain areas 7from limestone7 ,quartzite 7from sandstone7 ,gneiss 7from granite or sandstone7 ,schist 7from shale or basalt7 ,geologists arrange rocks in their chronologic sequence by studying the fossils and minerals which they contain4 ,the age of some rocks can be determined with reasonable precision from ratios of radioactive minerals and their fission products4 ,the relative age of others can be determined from their position1 the fossils enclosed in them1 and many minor details of their structure4 ,the stratigraphic column shown opposite may be thought of as a calendar by which geologic events in ,colorado can be arranged in their proper order and related to events in the rest of the world4 ,mississippian and ,pennsylvanian ,periods are ,american divisions2 elsewhere this time interval is known as the ,carboniferous ,period4 ,other time terms are in worldwide use4 ,in the generalized geologic map of ,colorado which accompanies ,chapter ,,ii1 rocks are identified by the era in which they were formed4 ,a more detailed geologic map can be obtained from the ,u4,s4 ,geologic ,survey map distribution center in the ,federal ,building1 ,denver4 ,illustration3 ,stratigraphic ,column ,,era ,period ,millions ,distinctive fossils ,events in ,colorado of years ago ,,cenozoic 7,age of ,mammals7 ,quaternary ,modern types of ,development of present animals and plants topography2 glaciation in mountains #c ,tertiary ,mammals1 flowering ,uplift and mountain plants building #gj ,,mesozoic ,dinosaurs and other 7,age of ,reptiles7 reptiles ,cretaceous ,submergence1 then uplift #ace ,jurassic ,desert1 then submergence #ahj ,triassic ,widespread floodplains and deserts #bbe ,,paleozoic 7,age of ,fishes7 ,permian ,first reptiles ,widespread floodplains and deserts #bgj ,pennsylvanian ,swamp and forest 8,ancestral ,rocky plants ,mountains0 #caj ,mississippian ,reef corals1 sharks ,partial submergence #cej ,devonian ,armored fish1 first ,probable submergence insects #djj ,silurian ,corals and shellfish ,probable submergence #ddj ,ordovician ,first fish ,submergence #ejj ,cambrian ,first hard-shelled ,gradual encroachment of animals sea from west #egj ,,precambrian 8,lipalian ,interval0 ,erosion to almost flat surface or peneplain ,primitive ,alternate episodes of soft-bodied marine mountain building and organisms erosion #c1fjj plus ,,the ,,prairies ,beneath the flat prairies of eastern ,colorado1 sedimentary rocks form a series of layers4 ,those near the surface are among the youngest rocks in ,colorado4 ,we know this from the fossils they bear1 fossils of large mammals such as the hairy mammoth1 which lived in early ,quaternary time1 the bison1 and many smaller mammals living today4 ,the layers below--sandstones1 shales1 and limestones--become progressively older as one goes deeper4 ,most of them were formed originally on the bottoms of shallow seas that covered this part of ,north ,america several times during the history of the continent4 ,in most places the layers are horizontal or nearly so1 but westward1 as they approach the mountains1 they bend upward1 gently at first and then more steeply4 ,at the very edge of the mountains1 where they were dragged upward when the mountains rose1 their eroded edges appear at the surface4 ,the entire sequence of flat-lying rocks can be studied where they are exposed along the mountain front or where streams and rivers have dissected them4 ,they are also known from cuttings and cores of oil and water wells4 ,some parts of ,colorado's eastern plains have been drilled so intensively in the search for oil and gas that we know a great deal about the subsurface sedimentary rock and can even make maps showing the distribution and character of the individual rock layers4 ,from such maps1 the history of the region can be deduced4 ,we know1 for example1 that the area around ,denver has subsided more in the past than has the area near ,la ,junta or ,lamar2 it is called the ,denver ,basin because of its past history and not because it is a basin at present4 ,although the plains of ,colorado appear flat1 they really slope gently eastward4 ,the rock layers near the surface slope eastward also1 but the deeper rock layers may not4 ,near the western edge of the ,plains ,province1 hills and valleys are formed by differential erosion of hard and soft rock layers4 ,some hills1 such as ,castle ,rock1 are topped with resistant sandstone2 others1 like ,mesa de ,maya south of ,trinidad and ,table ,mountain near ,golden1 are capped with layers of basalt4 ,close to the mountains flat-topped foothills result from partial dissection of former erosion surfaces as the mountains1 stabilized for a time1 rose again1 or as climatic cycles changed4 ,examples of these dissected erosion surfaces can be seen north and south of ,boulder4 ,far east of the mountain front1 near the northern border of ,colorado1 remnants of another1 higher prairie surface stand as ,pawnee ,buttes4 ,torrential erosion--spring floods and summer thunderstorms--has deeply furrowed the prairie surface here and left these buttes as lonely sentinels4 ,illustration3 ,this map shows the distribution1 character1 and thickness of certain ,jurassic rocks in ,colorado4 ,these rocks are deeply buried beneath the plains and are known there only from well samples4 ,they have been eroded from most mountain areas4 ,they come to the surface along the edges of the mountains and in the deeply incised canyons of the ,plateau ,province4 ,,precambrian ,,rocks ,,paleozoic ,,rocks ,,jurassic ,,rocks ,,sandstone ,,shaly ,,sandstone ,,sandy ,,shale ,,shale ,,jurassic ,,rocks ,,covered ,,with ,,volcanics ,,or ,,never ,,deposited4 ,what lies below the sedimentary layers of the plains8 ,the sedimentary rocks are #e1jjj to #aj1jjj feet thick4 ,they lie on an almost horizontal surface of much1 much older rock1 the ,precambrian or 8basement0 rock4 ,this is igneous and metamorphic rock1 much crumpled and folded1 the roots of long gone mountains which were beveled and leveled to an almost flat surface or peneplain perhaps a billion years ago4 ,we know little of the ancient basement rocks below the sedimentary layers of the plains1 for few wells penetrate this deep4 ,what we do know indicates that they are similar to rocks of the mountain masses to the west1 and are composed of granite1 schist1 and gneiss4 ,they probably are not rich in valuable minerals1 however1 for the mineral-rich veins of the mountains came about as a result of uplift of the mountain areas4 ,,the ,,peaks ,most of the individual ranges making up the ,rocky ,mountains in ,colorado are the result of highly localized movements of the crust as the entire region was thrust upward from below4 ,these movements broke the deep1 massive igneous and metamorphic rocks of the ,precambrian basement1 and bent the more flexible ,paleozoic and ,mesozoic layered rocks above them until they arched upward in a series of corrugations4 ,the mountains thus formed are known to geologists as faulted anticlines4 ,as the mountains rose1 they were of course attacked by the forces of erosion4 ,the sedimentary layers were completely stripped from the crests of many of the uplifts1 so that ,precambrian rocks were exposed4 ,it is these rocks which form the summits of the highest peaks of ,colorado4 ,as with all rules1 there are exceptions3 the ,spanish ,peaks are volcanic1 and the crest of the ,sangre de ,cristo ,range is composed of sedimentary rocks4 ,the trend of most of the ranges in ,colorado is north-south1 swinging to northwest-southeast near the southern end4 ,surprisingly1 in the northwestern corner of the state there is an east-west trending range1 the ,uinta ,mountains4 ,fifty or more mountain ridges in ,colorado have been named as separate ranges4 ,of these1 the most prominent1 frequently visited ones will be discussed here4 ,front ,range ,the easternmost range of the ,rocky ,mountains is the longest continuous uplift in the state4 ,it is a relatively simple faulted anticline extending from ,canon ,city northward to the ,wyoming border1 where it splits into two ridges1 the ,medicine ,bow ,mountains and the ,laramie ,range4 ,illustration3 ,longs ,peak challenges technical climbers with its #bjjj-;foot vertical east face1 the ,diamond4 ,this magnificent cliff is the result of glacial action and freezing and thawing in homogeneous but fractured granite4 ,the small remnant of ice and snow at the lower left is all that remains of the glacier4 ,the flat summit may be part of an ancient erosion surface formed toward the end of ,precambrian time4 7,jack ,rathbone photo7 ,along the highest portion of the range1 from ,pikes ,peak to ,rocky ,mountain ,national ,park1 the ,paleozoic and ,mesozoic sediments formerly draped over the top of the range have long since been washed away1 leaving only the gneiss1 granite1 and schist of the mountain core4 ,the almost flat tops of ,longs ,peak1 ,mt4 ,evans1 and ,pikes ,peak1 and the rolling upland traversed by ,trail ,ridge ,road in ,rocky ,mountain ,national ,park are thought to be remnants of the #fjj-million-year-old erosion surface that once existed at the top of the ,precambrian rocks1 and that still exists below the sedimentary rocks of the ,plains ,province4 ,this surface1 formed near sea level1 has been raised #ab1jjj to #ad1jjj feet within the ,mountain ,province4 ,throughout most of its length1 the ,front ,range displays some of the most striking high-altitude scenery in the world4 ,particularly accessible areas1 well worthy of visits1 are ,rocky ,mountain ,national ,park1 ,berthoud and ,loveland ,passes1 ,mt4 ,evans1 and ,pikes ,peak4 ,in these areas the ,precambrian rocks can be seen and studied1 and the effects of glaciation observed4 ,the granite1 gneiss1 and schist of the mountain core are shattered and broken into blocks of various sizes4 ,the breaks between the blocks are called joints if there is no apparent displacement between adjacent blocks1 and faults where there is obvious displacement4 ,the joints frequently appear in parallel arrays or sets2 there may be two or more intersecting sets1 giving a cross-hatched appearance to large exposures4 ,illustration3 ,east-west profile across ,rocky ,mountain ,national ,park1 through ,grand ,lake and ,longs ,peak1 showing the inferred position of the original surface of the anticlinal uplift of the ,front ,range4 ,this diagram is generalized1 and faults are not shown4 7,,usgs ,bull4 #gcj;a7 ,restoration of surface which emerged from ,cretaceous sea ,restoration of ,dakota sandstone ,,middle ,,park ,grand ,lake ,longs ,peak ,foothills ,,great ,,plains ,sedimentary rocks ,granite and schist ,sedimentary rock of plains ,south ,platte ,r4 ,illustration3 ,big ,thompson ,canyon1 west of ,loveland on ,u4,s4 highway #cd1 is carved in almost vertical layers of ,precambrian metamorphic rocks4 ,gently dipping ,late ,paleozoic and ,mesozoic sedimentary rocks of the ,fountain1 ,lyons1 ,lykins1 and ,morrison ,formations can be seen in the distance1 capped by the ,cretaceous ,dakota ,sandstone4 7,floyd ,walters photo7 ,the ,precambrian rocks vary from place to place4 ,several irregular masses of granite1 called batholiths1 make up portions of the range4 ,batholiths are large intrusions of molten rock that cooled slowly at great depth4 ,the minerals in them form distinct crystals1 often quite large4 ,the ,pikes ,peak ,granite and the ,boulder ,creek ,granite are examples4 ,highly contorted and banded gneiss and schist are well exposed elsewhere1 particularly in the ,idaho ,springs-,central ,city-,black ,hawk region4 ,along the flanks of the ,front ,range1 the eroded edges of the sedimentary rocks which once covered the range are exposed4 ,these rocks are usually tilted sharply against the mountains1 as at ,garden of the ,gods1 ,denver's ,red ,rocks ,park1 and the ,flatirons near ,boulder4 ,the ,rocky ,mountain ,association of ,geologists has erected a plaque explaining the geology of the ,red ,rocks area2 look for it about half a mile northeast of the ,red ,rocks ,amphitheater4 ,tilted layers of ,paleozoic and ,mesozoic sandstones form hogback ridges along the mountain front1 and stand out clearly on aerial photographs4 ,in some areas1 particularly near ,boulder1 ,coal ,creek1 and ,golden1 the tilting of the sedimentary layers has been so extreme that the layers are upside down4 ,basement rocks may even be thrust out above them4 ,illustration3 ,sandstones and conglomerates of the ,pennsylvanian ,fountain ,formation dip steeply toward the plains along the eastern edge of the ,rockies4 ,near ,denver1 erosion has carved these rocks into a natural amphitheater1 now the site of ,red ,rocks ,amphitheater4 ,precambrian granite forms the hill in the background4 7,jack ,rathbone photo7 ,further north1 near ,loveland and ,lyons1 as well as further south at ,colorado ,springs1 irregularities in the uplift have caused abrupt breaks in the generally smooth eastern edge of the range4 ,folds and faults in these areas trend northwest1 cutting across and offsetting the mountain front4 ,illustration3 ,south of ,colorado ,springs1 between ,fort ,carson and the ,,norad installation in ,cheyenne ,mountain1 ,mesozoic rocks are faulted against the mountain front4 ,paleozoic rocks are deeply covered by as much as #cjjj feet of ,mesozoic sediments4 ,they come to the surface about #aj miles further south4 ,,rampart ,,range ,garden of the ,gods ,ute ,pass ,fault ,,manitou ,,springs ,,pikes ,,peak ,,massif ,,cheyenne ,,mountain ,,colorado ,,springs ,,cross ,,section ,ute ,pass ,fault ,rampart ,fault ,tertiary ,mesozoic ,paleozoic ,precambrian ,illustration3 ,west of ,boulder1 several intersecting sets of joints pattern the ,precambrian rocks above ,boulder ,creek4 7,john ,chronic photo7 ,the west margin of the ,front ,range is not as sharply defined as the eastern margin4 ,prominent faults edge ,north1 ,middle1 and ,south ,parks1 however4 ,the northern end of the range merges with the ,medicine ,bow ,mountains1 where dips of sedimentary rocks seldom exceed #cj to #dj degrees4 ,at its southern end1 the ,front ,range plunges into the plains1 although a southwest-trending ridge connects it with the ,wet ,mountains4 ,within the ,precambrian core of the ,front ,range1 many economic mineral deposits have been found4 ,these are discussed in ,chapter ,,iii4 ,glacial features of the ,front ,range are discussed in ,chapter ,,ii in the section on the ,quaternary ,period4 ,wet ,mountains ,the ,wet ,mountains are the easternmost range of the ,rockies south of ,canon ,city4 ,their crest has a distinct northwest-southeast trend1 with the north end offset about #be miles westward from the south end of the ,front ,range4 ,the ,canon ,city ,embayment lies at the junction between the ranges4 ,though smaller and lower than the ,front ,range1 the ,wet ,mountains include many pleasant and easily accessible recreation areas and a number of attractive streams and reservoirs4 ,greenhorn ,peak1 the summit of the range1 is #ab1ccd feet high4 ,it is formed of ,precambrian granite1 as is most of the crest of the range4 ,the structure of the eastern side of the ,wet ,mountains is similar to that of the ,front ,range1 except that there are more faults in the sedimentary layers4 ,the southern end plunges southeastward into the plains4 ,on the western side1 westward-dipping sediments are completely submerged in ,cenozoic lava flows and debris from the mountains4 ,ore minerals very like those of the ,front ,range occur near ,silver ,cliff1 but they have so far proved to be of little economic importance4 ,sangre de ,cristo ,range and ,spanish ,peaks ,the ,sangre de ,cristo ,mountains are visible from many parts of southeastern ,colorado as a jagged1 sawtoothed1 snow-crested ridge on the western skyline4 ,they extend about #aej miles from the ,arkansas ,river near ,salida southward into ,new ,mexico4 ,few mountain ranges form so impassable a barrier as the ,sangre de ,cristos4 ,only at ,la ,veta ,pass does a highway cross the range4 ,however1 old wagon roads1 passable now by jeep or on foot1 once existed across ,hayden1 ,music1 ,mosca1 and ,whiskey ,creek ,passes4 ,often no more than twenty miles wide1 the central portion of the range is composed largely of red ,late ,paleozoic sediments like those exposed in the ,garden of the ,gods and ,red ,rocks ,park4 ,these rocks are intricately folded and faulted1 but not metamorphosed4 ,they include sandstones1 shale1 conglomerates1 and fossil-bearing limestones4 ,the northern end of the range is formed of ,precambrian igneous and metamorphic rocks4 ,just west of ,la ,veta ,pass1 ,sierra ,blanca stands as an outpost of the range where its continuity is interrupted and its structure changed4 ,huge blocks of ,precambrian granite were here pushed upward and thrust westward to form a cluster of peaks1 several of which are over #ad1jjj feet in elevation4 ,many prominent rock glaciers are present in the ,sangre de ,cristo ,mountains4 ,they are composed of fragments of rock1 lubricated by snow and ice1 creeping almost imperceptibly down the steep flanks of the high peaks4 ,one of these rock glaciers can be seen on the slope of ,mt4 ,mestas east of ,la ,veta ,pass2 others are visible from ,great ,sand ,dunes ,national ,monument4 ,south of ,la ,veta ,pass1 an igneous intrusion along the axis of the range changes the character of the ,sangre de ,cristos4 ,this intrusion is harder and has weathered more slowly than the rest of the range1 and forms a group of prominent peaks known as the ,culebra ,range4 ,on the west flank of the ,sangre de ,cristo ,range1 east of ,villa ,grove1 a prominent iron-mineralized area can be seen4 ,here the ghost mine of ,orient marks the site where iron ores were mined in the early days of the ,colorado ,fuel and ,iron ,company4 ,nearby1 an abrupt terrace along the edge of the valley marks the position of a fault4 ,recent gravels are involved in this fault1 indicating that movement has taken place here within the last few hundred years4 ,a number of hot springs occur along the base of the mountains nearby4 ,the ,spanish ,peaks1 not structurally related to the ,sangre de ,cristos1 are visible from ,la ,veta ,pass highway4 ,these two peaks represent a pair of ,cenozoic volcanoes1 now deeply eroded and much reduced from their former height4 ,numerous dikes radiating from the bases of these peaks represent fissures which were filled with lava as the peaks formed4 ,the ,great ,sand ,dunes1 close to the ,sangre de ,cristo ,mountains north of ,sierra ,blanca1 are discussed in ,chapter ,,ii in the section on the ,quaternary ,period4 ,illustration3 ,spanish ,peaks1 south of ,colorado ,springs and southwest of ,walsenburg1 are twin mountains of volcanic and intrusive rock1 the roots of ,tertiary volcanoes greatly worn down and reshaped by erosion4 ,this view looks southeast from near ,la ,veta ,pass1 on ,u4,s4 ,highway #afj4 7,jack ,rathbone photo7 ,park ,range and ,rabbit ,ears ,range ,bordering the western side of ,north1 ,middle1 and ,south ,parks1 another long north-south trending ridge extends from the ,wyoming border toward the center of ,colorado4 ,the northern part of this ridge1 forming the western boundary of the main mountain mass in the state1 is called the ,park ,range4 ,the structure of the ,park ,range is similar to that of the ,front ,range3 a huge linear corrugation in the earth's crust1 bounded by faults4 ,because this area has fewer resistant sedimentary rock layers above the ,precambrian basement rocks1 it is not prominently edged with upturned sedimentary layers4 ,illustration3 ,hahn's ,peak1 a highly eroded laccolith of rhyolite porphyry1 lies on the west side of the ,park ,range1 along the eastern margin of the ,plateau ,province4 ,placer gold was discovered here in #ahfe1 but the bedrock source of the gold was never found4 7,jack ,rathbone photo7 ,a geologic section shows the structure of the area4 ,,tertiary ,,red ,,beds ,,jurassic ,,dakota ,,mancos ,,dakota ,hahn's ,peak ,,porphyry ,,mancos ,,dakota ,,porphyry ,,jurassic ,,red ,,beds ,,re-,,cambrian ,illustration3 ,hahn's ,peak ,the range is crossed by ,rabbit ,ears ,pass in the north2 ,gore ,pass near ,kremmling marks its southern end4 ,mt4 ,zirkel 7#ab1ahj feet7 and ,flattop ,mountain 7#ab1aah feet7 are the two high points of the range2 these and a number of unnamed peaks over #aa1jjj feet high are upward-faulted blocks of ,precambrian granite4 ,a rough ridge of volcanic country joins the ,park ,range with the ,front ,range and effectively separates ,north ,park and ,middle ,park4 ,this is the ,rabbit ,ears ,range1 named for a double-eared knob of ,precambrian granite near ,rabbit ,ears ,pass on ,u4 ,s4 highway #dj4 ,many ,tertiary volcanic features1 including dikes and lava flows1 can be seen along this ridge1 which is also traversed by ,colorado state highway #abe between ,granby and ,walden via ,willow ,creek ,pass4 ,gore ,range ,the ,gore ,range lies south of ,gore ,pass1 along the ,park ,range trend4 ,the ridge of this range is low for about #ae miles south of ,kremmling1 but the southern part of the range forms a spectacular high cluster of peaks with many relatively inaccessible and rugged summits4 ,many of the peaks in this remote country are as yet unnamed2 the area has been set aside as the ,gore ,range-,eagle's ,nest ,wilderness ,area4 ,the ,colorado ,river cuts directly across the northern part of the ,gore ,range just west of ,kremmling1 in a steep-walled canyon that is one of the wild scenic spots of ,colorado4 ,illustration3 ,the southern part of the ,gore ,range1 viewed from the east1 shows ,precambrian granite and metamorphic rocks rising above ,cretaceous shale hills4 ,the nearly horizontal crest of the range probably represents the ,precambrian erosion surface4 7,jack ,rathbone photo7 ,the ,gore ,range is1 like the ,front ,range1 a faulted anticline with ,precambrian rocks at its core4 ,the red sedimentary rocks on the west flank of the range1 visible at ,vail ,pass and ,vail ski area1 are of the same age as those in ,red ,rocks ,park near ,denver and the ,garden of the ,gods near ,colorado ,springs4 ,paleozoic rocks are absent on the east flank of the range1 having been eroded from that area before ,mesozoic deposition4 ,south of the ,colorado ,river and north of the ,wilderness ,area1 ,mesozoic rocks extend over the crest of the range4 ,the south end of the ,gore ,range is marked by ,tenmile ,gorge 7,u4 ,s4 highway #f between ,frisco and ,vail ,pass74 ,this gorge is a glacial valley1 carved during the ,ice ,age by a glacier more than #a1jjj feet thick1 along a weak faulted zone in the range4 ,a fault surface can be seen on the east side of the valley4 ,from ,vail ,pass1 or from the top of the ,vail ski lift1 other evidences of glaciation can be seen--cirques and ,u-shaped valleys--testifying to the former presence here of many large valley glaciers4 ,tenmile and ,mosquito ,ranges ,with scarcely a break1 the ,park ,range-,gore ,range structure continues southward into the ,tenmile and ,mosquito ,ranges4 ,these high ridges separate ,south ,park from the upper ,arkansas ,valley1 and include a cluster of very high peaks1 ,quandary1 ,mt4 ,lincoln1 ,mt4 ,democrat1 and ,mt4 ,bross1 all over #ad1jjj feet in elevation4 ,structurally1 both the ,tenmile ,range and the ,mosquito ,range are highly asymmetrical anticlines1 gentle on the east and steeply faulted on the west4 ,paleozoic sedimentary rock layers containing many fossils cover large portions of the higher parts of these ranges1 but two of the highest peaks1 ,mt4 ,bross and ,mt4 ,lincoln1 are capped by the ,lincoln ,porphyry1 a ,tertiary intrusive1 while ,quandary ,peak is ,precambrian granite4 ,these mountains are highly mineralized1 and have been extensively explored and mined4 ,the ,climax ,molybdenum ,corporation operates an especially large mine at ,climax1 and the ,new ,jersey ,zinc ,company has a large underground mine and mill at ,gilman1 on the western slopes of ,tenmile ,range4 ,buffalo ,peaks1 two highly eroded volcanic mountains near the south end of ,mosquito ,range1 are extrusions of lava and ash which have buried the axis of the ,mosquito uplift4 ,they are major volcanoes related to a group of small volcanic cones near ,antero ,junction1 in ,south ,park4 ,south of ,buffalo ,peaks1 near ,trout ,creek ,pass1 the ,mosquito ,range loses altitude rapidly and merges with the rough country called the ,arkansas ,hills4 ,cinder cones1 dikes1 and other evidences of ,tertiary volcanic activity can be seen between ,trout ,creek ,pass and ,salida4 ,sawatch ,range ,bordering the ,arkansas ,river valley on the west1 the ,sawatch ,range includes ,colorado's highest mountain1 ,mt4 ,elbert 7#ad1dag feet74 ,with several other #ad1jjj-;foot summits1 this range is the highest in the state4 ,one group of peaks1 known as the ,collegiate ,range 7,mts4 ,harvard1 ,yale1 ,columbia1 and ,princeton7 forms a particularly imposing vista from ,u4 ,s4 highway #bd between ,trout ,creek ,pass and ,buena ,vista4 ,the ,independence ,pass highway 7,colorado #hb7 between ,leadville and ,aspen penetrates the heart of the ,sawatch high country4 ,the ,sawatch ,range as a whole is about #ajj miles long 7north to south7 and #dj miles wide4 ,it is a great faulted anticline intruded by igneous rocks4 ,the high area north of ,leadville shows that the ,sawatch and ,mosquito ,ranges are in reality one huge dome with a slight sag in the middle4 ,the ranges1 though1 are sharply separated topographically by the deep valley of the ,arkansas ,river4 ,precambrian rocks are near the surface between the ranges1 hidden only by a thin cover of stream gravels4 ,near ,leadville1 some complexly faulted ,paleozoic limestones lie in the sag between the ranges4 ,at ,mt4 ,princeton ,hot ,springs there is evidence of repeated faulting and igneous activity4 ,the rocks are strongly altered by hot water coming to the surface through fissures and cracks4 ,on the west side of the ,sawatch range1 the old mining towns of ,tincup and ,aspen grew up where limestone and sandstone layers1 broken and crumpled as the ,sawatch ,range rose1 were mineralized by solutions rich in gold and silver4 ,the ,aspen ,mining ,district was studied extensively by geologists of the ,u4,s4 ,geological ,survey1 and their maps show almost unbelievable complexity in the faulting of the rock layers which exist there4 ,the north end of the ,sawatch ,range plunges under shales and sandstones along the ,eagle ,river east of ,wolcott4 ,gypsum in the sediments here has acted like putty3 the layers of rock in which it was deposited have become peculiarly crumpled1 making the area along the ,eagle ,river 7visible from ,u4 ,s4 ,interstate #gj7 between ,avon and ,edwards hummocky and irregular4 ,vegetation is unusually sparse here because of gypsum in the soil4 ,about midway between ,edwards and ,wolcott1 the ,eagle ,river suddenly changes direction and flows northward for about a mile before resuming its former westward course4 ,this sudden change is caused by a sharp north-south fold in the sedimentary rocks on the northwestern flank of the ,sawatch ,range4 ,a magnificent series of roadcut and hillside exposures along the highway here illustrates the close relation between rock layers and river course4 ,within about a mile1 the highway cuts through rocks of ,pennsylanian1 ,permian1 ,triassic1 ,jurassic1 and ,cretaceous age1 spanning a geologic time interval of more than #bjj million years4 ,the south end of the ,sawatch ,range1 at ,monarch ,pass1 contains steeply dipping ,late ,paleozoic limestones and coal beds4 ,the coal has been mined on a small scale2 the limestone is now quarried for use as a flux in iron smelters at ,pueblo4 ,illustration3 ,the area below the ,aspen ,mountain ski lift is highly complex geologically4 ,it is particularly well known because of extensive prospecting and mining activity in the region4 ,elk ,mountains and ,west ,elk ,mountains ,the ,elk ,mountains and ,west ,elk ,mountains appear to be westward continuations of the ,sawatch ,range4 ,structurally1 however1 they are not faulted anticlines like most of the other ranges in ,colorado1 but are composed of a series of layers of ,paleozoic sediments thrust westward over one another4 ,these rocks1 often crumpled and highly metamorphosed1 are cut by numerous sills1 dikes1 and other intrusions1 many of which have caused mineral enrichment locally4 ,at ,maroon ,bells1 in the canyon of ,maroon ,creek1 and at ,redstone on the ,crystal ,river1 these metamorphosed sediments are well exposed4 ,here1 red sandstones and shales have been altered to quartzites and slate4 ,at ,marble1 metamorphism of a thick limestone bed has produced white marble of great beauty1 known as ,yule ,marble4 ,this decorative stone was quarried extensively until about #aidj4 ,it was used in the ,lincoln ,memorial and several other monumental structures2 in the town of ,marble it has been used for the doorsteps of log cabins6 ,the largest block quarried1 for the ,tomb of the ,unknown ,soldier in ,arlington ,national ,cemetery1 measured #ad by #g4d by #f feet in the rough1 and weighed #ef tons4 ,illustration3 ,mt4 ,sopris1 south of ,glenwood ,springs1 is an igneous intrusion4 7,jack ,rathbone photo7 ,crested ,butte1 at the south end of the ,elk ,mountains1 is a small intrusive igneous mass called a laccolith4 ,hard and resistant to erosion1 it stands over #b1jjj feet above the adjacent valley floor4 ,san ,juan ,mountains ,the ,san ,juan ,mountains are the most extensive range in ,colorado1 and also the most heterogeneous4 ,covering more than #aj1jjj square miles of the southwestern part of the state1 these mountains are formed mostly of ,tertiary volcanic rocks1 the result of repeated outpourings of lava and ash from a cluster of volcanoes4 ,water-laid gravels composed of volcanic sand and pebbles are interlayered with basalts and ash beds2 the total thickness of these beds reaches many thousands of feet4 ,illustration3 ,the mining town of ,ouray1 now also a tourist haven and summer resort1 nestles below ,pennsylvanian sedimentary rocks of ,ouray ,canyon4 ,at the north end at town can be seen the ,ouray ,hot ,springs swimming pool4 ,gold1 silver1 lead1 and zinc are still mined in this area4 7,jack ,rathbone photo7 ,the widespread volcanic activity which formed most of the range began in mid-,tertiary time and continued for several million years4 ,a few ,quaternary volcanic flows are known in the region1 but there is no active volcanism there at present4 ,the western side of the main range1 including some of the highest peaks1 consists primarily of uplifted and faulted ,paleozoic sedimentary layers4 ,these layers1 highly dissected by erosion1 can be seen near ,ouray1 at ,molas ,lake1 and at ,durango4 ,large patches of ,precambrian granite and metamorphic rocks protrude through the sediments1 as in the ,needle ,mountains2 they indicate that this part of the range is a faulted anticline like many other ,colorado ranges4 ,early ,cenozoic glacial deposits occur in some parts of the ,san ,juans4 ,these are unusual features1 as glaciation of this age is unknown elsewhere in ,colorado4 ,three small ranges rise just west of the ,san ,juans3 the ,san ,miguel1 ,rico1 and ,la ,plata ,mountains4 ,each consists of several small masses of ,tertiary igneous rock intruded into ,paleozoic conglomerates1 shales1 and limestones4 ,mineralization has been intense in the ,san ,juans2 most of it took place during the ,late ,tertiary volcanic period4 ,rich veins penetrate ,precambrian gneiss and granite1 and ,paleozoic limestones are often enriched also4 ,several mines are still active near ,ouray1 ,silverton1 ,telluride1 and ,rico4 ,uinta ,mountains ,the eastern end of ,utah's ,uinta ,mountains extends into ,colorado4 ,unlike other ranges in ,colorado1 these mountains trend east-west4 ,structurally1 the range is a faulted anticline4 ,it is quite asymmetrical1 however1 and is tilted and folded upward on the south1 and overturned or thrust-faulted on the north4 ,steeply dipping ,mesozoic and ,paleozoic sediments on the south side of the range1 sparsely vegetated and often thrown into spectacular folds1 are a prominent feature of northwest ,colorado scenery4 ,in ,colorado the crest of the ,uintas reaches an elevation of about #h1ejj feet4 ,it consists of ,precambrian rocks1 but these are not the igneous and metamorphic rocks that characterize the ,precambrian core of other ,colorado mountains4 ,they are easily recognized as sediments--dark red conglomerates1 sandstones1 and mudstones--virtually unmetamorphosed though they were deposited nearly a billion years ago4 ,called the ,uinta ,mountain ,formation1 these rocks are found only in this part of ,colorado and adjacent areas of ,utah4 ,they are probably related to similar ,precambrian rocks found in ,montana and ,canada4 ,at the east end of the ,uintas two isolated uplifts1 ,cross ,mountain and ,juniper ,mountain1 are faulted blocks of ,paleozoic rocks standing like islands in a sea of ,cenozoic valley fill4 ,they are the last outposts of the ,uinta anticlinal pattern as it wanes toward the southeast4 ,dinosaur ,national ,monument1 a ,uinta ,mountain tourist attraction1 encompasses a vast area of wilderness on both sides of the ,yampa ,river in ,colorado4 ,here many of the features of the east end of the ,uinta ,mountain structure can be seen4 ,a unique display of the world's largest fossils can be visited in the ,utah portion of the ,monument4 ,illustration3 ,at their confluence in ,dinosaur ,national ,monument1 the ,yampa and ,green ,rivers have carved ,late ,paleozoic sandstone into the precipitous cliffs of ,steamboat ,rock4 7,william ,c4 ,bradley photo7 ,,the ,,plateaus ,the western quarter of ,colorado is a region of flat-lying ,paleozoic1 ,mesozoic1 and ,cenozoic sedimentary rocks which have not been bent up into mountains except in a few isolated instances4 ,this area lies more than a mile above sea level1 however1 and because of the gradient such an elevation affords1 it is deeply sculptured4 ,the ,colorado ,river and its tributaries have sliced into the plateau surface1 separating it into many isolated tablelands or mesas4 ,some are capped with sedimentary rock1 others with ,tertiary basalt4 ,illustration3 ,the ,grand ,hogback is a good example of the type of geologic structure known as a monocline4 ,the hogback ridge is formed by differential erosion1 where soft layers wear away more easily than hard layers4 ,simple folds and faults have given the mesas different elevations4 ,thus the average elevation of the ,white ,river ,plateau is #aa1jjj feet1 that of the ,roan ,plateau #i1ejj feet1 and that of ,mesa ,verde only #g1jjj feet4 ,west of ,durango the plateaus dip gently southward1 as can be seen at ,mesa ,verde4 ,igneous intrusions and extrusions have altered plateau topography in some areas4 ,west of ,mesa ,verde1 for instance1 an intrusive stock forms a prominent dome in the ,southern ,ute ,indian ,reservation4 ,west of the northern ,colorado mountains1 and north and west of the ,white ,river ,plateau1 a rolling upland extends from ,colorado into ,utah and ,wyoming4 ,it is interrupted by the ,uinta ,mountains and a number of smaller related uplifts such as ,juniper ,mountain and ,cross ,mountain4 ,south of the ,uinta axis the area is known as the ,uinta ,basin4 ,the northern part of this area is structurally the south edge of the ,green ,river or ,washakie ,basin in ,wyoming4 ,the ,rangely anticline1 in the northeastern corner of the ,uinta ,basin1 is one of ,colorado's richest oil fields2 it is discussed in ,chapter ,,iii4 ,although surfaced with much younger sediments than the rest of the ,plateau ,province1 this area is structurally similar4 ,on the whole1 sedimentary layers are relatively flat-lying1 and where they are uplifted they are deeply sculptured by streams and rivers4 ,the sedimentary rocks in this region contain uranium and placer gold in addition to great oil and gas deposits4 ,the southeastern part of the ,uinta ,basin1 usually called the ,piceance ,basin1 is the site of a great deposit of oil shale 7see ,chapter ,,iii74 ,the term 8basin0 may here seem unusual to the casual observer1 for the oil shales occur on the ,roan ,plateau at places well over #aj1jjj feet in elevation4 ,however1 the entire region was basin-like--lower than the surrounding ranges--for many millions of years1 and during ,tertiary time thousands of feet of valley and lake deposits were laid down in it4 ,the ,white ,river ,plateau1 north of ,glenwood ,springs1 is composed of almost horizontal ,paleozoic sedimentary rocks that fold downward sharply along its south and west edges4 ,the fold is #ace miles long and is clearly marked by the ,grand ,hogback1 the eroded edge of hard ,cretaceous and early ,cenozoic rock layers4 ,shale and coaly layers involved in the same fold have eroded more readily1 leaving the resistant sandstone as a prominent ridge4 ,the ,uncompahgre ,plateau1 southwest of ,grand ,junction1 is structurally very like the ,white ,river ,plateau4 ,its features can be well observed in ,colorado ,national ,monument4 ,it has been elevated several thousand feet more than the ,book ,cliffs and ,grand ,valley areas to the north4 ,sharp folding and faulting near the ,colorado ,river at the north boundary of the ,national ,monument show that differential movement between the two regions was sharp and localized4 ,a series of northwest-trending anticlines along the ,utah border in southwestern ,colorado are of special geologic interest4 ,they represent peculiar structures in which salt and gypsum have played a major part4 ,these minerals were deposited in thick layers late in ,paleozoic time2 subsequently they were covered by thousands of feet of sand1 shale1 and limestone4 ,because of their low density and high plasticity they have since crept upward along weak spots in the overlying sediments1 often contorting these rocks as they moved4 ,breaking through to the surface1 the salt and some of the gypsum washed away more rapidly than the surrounding rock1 leaving long faulted troughs such as ,gypsum ,valley and ,paradox ,valley4 ,in most of these structures the gypsum can still be seen1 although the more soluble salt has eroded away4 ,oil wells in this part of ,colorado and in adjacent parts of southeast ,utah have penetrated thousands of feet of evaporites1 including pure salt1 gypsum1 and potassium salts4 ,illustration3 ,in the arid climate of the ,colorado ,plateaus1 ledges of well-cemented sandstone stand out sharply from slopes of shale or mudstone4 ,the ,mesa ,verde and ,mancos ,formations1 ,cretaceous in age1 form the slopes and top of ,mt4 ,garfield near ,grand ,junction 7,jack ,rathbone photo7 ,the peculiar weathering characteristics of flat-lying sedimentary rocks in an arid climate are well demonstrated in ,colorado ,national ,monument1 ,mesa ,verde ,national ,park1 and elsewhere in the ,plateau ,province4 ,those fortunate enough to make a river trip through the ,yampa or ,green ,river ,canyons in northwestern ,colorado or on the rivers of eastern ,utah and northern ,arizona will have an unusually fine opportunity to observe close at hand the weathering and erosion in this area4 ,resistant sandstone and limestone layers break into sheer cliffs1 often many hundreds of feet high1 while the softer layers of mudstone and shale form gentle slopes and terraces4 ,vast arching caves often develop where resistant layers are undermined--caves sometimes containing ancient ,indian dwellings4 ,,ii ,geologic ,history of ,colorado ,astronomical and geologic evidence indicates that the earth was probably formed as an immense blob of molten rock1 held together and shaped into spherical form by its own gravity4 ,it may even have been gaseous at first1 cooling gradually to a molten state4 ,after hundreds of millions of years it became cool enough to begin to harden4 ,as the surface cooled1 a crust formed1 and lay like a blanket over the liquid mass beneath4 ,convection currents--large-scale boiling movements--stirred the molten interior1 thrust portions of the crust upward1 and sucked other portions downward to be remelted4 ,some of the lighter components1 such as compounds of silicon and oxygen and hydrogen1 accumulated on the surface like froth on a kettle3 the continents were born4 ,with further cooling the atmosphere and oceans came into being4 ,something can be told of the age of the continents4 ,measurements of radioactivity in the most ancient rocks exposed at the surface today indicate that the oldest known continental rock is between three and four billion years old4 ,since the continents were formed1 they have been bent and shifted and broken by the pressures exerted against them by convection in the interior4 ,parts of the continents at times have been submerged below the level of the sea1 even as they are today4 ,other portions1 lifted above sea level1 were immediately attacked by the wearing-down processes of erosion4 ,the battle between mountain-building forces and erosion has been a continuous one ever since the crust was formed4 ,even now earthquakes give testimony to continued crustal movement1 storms still sweep across the continents and wash mud and frost-loosened rocks into churning torrents1 rivers still deposit great floodplains and deltas1 sediments accumulate slowly but persistently upon the bottoms of the seas4 ,,precambrian ,,era ,only part of the earth's very early history is represented in ,colorado1 where the oldest known rocks are the gneisses and schists of the ,idaho ,springs ,formation1 at least #a1hjj1jjj1jjj years old4 ,these rocks appear to be the remains of ancient sediments1 folded and metamorphosed into vast mountain areas long before recognizable life inhabited the earth4 ,precambrian rocks in ,colorado are on the whole very poorly known4 ,they have1 however1 been studied in detail in the ,front ,range west of ,denver and ,boulder1 where they have been intensively explored for valuable minerals4 ,the lack of fossils in the oldest rocks makes their close correlation difficult1 but from studies of radioactive minerals contained in these rocks1 and of the relationships of the rock units themselves1 we can list them in order of their relative ages4 ,note that the rock sequence given below reads chronologically from bottom to top--a logical pattern in geology since younger rocks1 especially those of sedimentary origin1 normally lie above older ones4 ,recent studies indicate that the sequence may be much more complex than shown here4 7youngest7 ,silver ,plume ,granite3 light pinkish gray1 fine-grained granite4 ,pikes ,peak ,granite3 pink1 coarse-grained granite4 ,boulder ,creek ,granite3 dark gray1 faintly banded granodiorite4 ,coal ,creek ,quartzite3 light gray quartzite with grains ranging in size from fine sand to boulders1 with some interbedded schist4 ,swandyke ,hornblende ,gneiss3 dark gray to black1 strongly banded gneiss4 7oldest7 ,idaho ,springs ,formation3 gray to black schist and gneiss4 ,from a sequence such as this1 it is possible to reconstruct some features of ,colorado's early history4 ,the first chapter of which we have a record is the deposition of the ,idaho ,springs ,formation1 probably as an accumulation of mud1 sand1 and limy mud in an ancient sea4 ,swandyke deposition followed--the sediments were iron-rich1 perhaps derived from ancient volcanic materials4 ,the original ,coal ,creek sediments were sands and gravels1 some of them quite coarse and therefore indicative of near-shore deposition4 ,the schist layers suggest that muds must have been deposited also4 ,illustration3 ,south of ,ouray1 ,cambrian sandstones of the ,sawatch ,formation lie almost horizontally across the vertical ,precambrian metamorphic rocks4 7,jack ,rathbone photo7 ,together these three formations represent some #dj1jjj feet of sedimentary layers4 ,deposition of such a great thickness of mud1 sand1 and lime must have taken a very long period of time4 ,details of the geography of the continent during that period have of course been obscured by later events1 when these rocks were subjected to repeated uplift1 crumpling1 folding1 various degrees of remelting and recrystallization1 and erosion4 ,but the ancient sediments must have been derived from even more ancient highlands1 either folded and faulted mountains or volcanoes1 and probably were deposited under water in broad expanses of sea that covered portions of the continent4 ,illustration3 ,geologic map of ,colorado4 ,geologic maps show the age of rocks appearing at the surface1 disregarding soil cover4 ,a more detailed geologic map of ,colorado may be obtained from the ,u4,s4 ,geological ,survey at the ,federal ,center in ,denver4 ,,precambrian ,,paleozoic ,,mesozoic ,,cenozoic ,,sediments ,,cenozoic ,,volcanics ,yampa ,river ,white ,river ,fort ,collins ,south ,platte ,river ,glenwood ,springs ,denver ,colorado ,river ,grand ,junction ,aspen ,gunnison ,river ,colorado ,springs ,gunnison ,salida ,dolores ,river ,rio ,grande ,arkansas ,river ,la ,junta ,walsenburg ,alamosa ,durango ,the ,boulder ,creek1 ,pikes ,peak1 and ,silver ,plume ,granites cut through the metamorphic rocks1 and are therefore younger4 ,they represent pulses of molten rock forced upward from deep within the crust1 probably during three separate episodes of mountain building4 ,as each set of mountains was formed1 it was worn down1 perhaps to low rolling hills1 perhaps to flat plains almost at sea level1 and partially or entirely covered with thick layers of sediment4 ,each time1 another mountain building episode followed1 with new intrusions of granite and new metamorphism of the pre-existing rocks4 ,each succeeding period of metamorphism and mountain building further changed the nature of the rocks involved1 complicating the patterns of folding and faulting1 adding recrystallization to recrystallization1 until the oldest of the rocks bore little trace of their original sedimentary nature4 ,in general1 the rocks that are oldest were most altered by the repeated metamorphism1 while the younger rocks were less altered4 ,illustration3 ,the ,black ,canyon of the ,gunnison ,river is one of the state's deep and spectacular chasms4 ,canyon walls are of ,precambrian gneiss intruded by many dikes and highly fractured by later uplifts4 ,the flat upper surface of the ,precambrian rocks represents an ancient plain on which1 during ,jurassic time1 the dinosaur-bearing ,morrison ,formation was deposited4 7,john ,chronic photo7 ,the ,precambrian ,era ended with a long period of erosion1 a period known to geologists as the ,lipalian ,interval4 ,during this time1 over almost the entire world there was no mountain building4 ,the land lay sleeping1 subject only to the forces of erosion4 ,the last mountains were flattened nearly to sea level4 ,slow1 sluggish streams and rivers carried sand and mud toward the oceans--oceans in which perhaps primitive1 soft-bodied organisms1 with no hard parts to be preserved as fossils1 were beginning to evolve4 ,on the continents1 the time of intense metamorphism was over2 most rocks of later eras are preserved today in pretty much their original state4 ,the boundary between the ,precambrian and later rocks is normally well defined4 ,it is visible at many places in ,colorado3 in ,williams ,canyon near ,colorado ,springs1 in ,glenwood ,canyon1 near ,red ,rocks west of ,denver1 just west of ,la ,veta ,pass1 at the top of ,royal ,gorge and the ,black ,canyon of the ,gunnison4 ,at most of these localities it is a smoothly beveled surface1 with highly contorted ,precambrian rocks below it and flat-lying ,paleozoic sediments above it4 ,near ,red ,rocks and ,la ,veta ,pass1 the same relationship prevails1 but the entire contact1 and the rocks above and below it1 have been steeply tilted by the uplift of the present mountains4 ,in portions of western ,north ,america1 deposition late in ,precambrian time has left a series of flat-lying rocks between the contorted ,precambrian and later ,paleozoic sediments4 ,these rocks can be seen in northwestern ,colorado1 where they form the dark red sedimentary core of the ,uinta ,mountains4 ,,paleozoic ,,era ,geologists have divided the second great era of geologic time into units called ,periods4 ,the rocks deposited during a ,period are called ,systems1 but more often than not it is convenient to discuss them in terms of easily recognized units of rock1 called ,formations4 ,formations are named after areas in which they are well exposed4 ,the stratigraphic column given in ,chapter ,i shows the ,periods and ,systems in their correct order1 and gives the age in years for each1 as determined by radioactivity methods4 ,as you read1 refer as often as necessary to this column4 ,the geologic map on page #ce will help you locate areas where the rocks discussed in the text are exposed1 and will greatly facilitate your understanding of the geology of the state4 ,illustration3 ,the ,cambrian ,sawatch ,sandstone lies almost horizontally on ,precambrian granite in ,glenwood ,canyon4 ,in the foreground is the ,colorado ,river4 7,jack ,rathbone photo7 ,cambrian ,period 7#ejj-egj million years ago7 ,the first fossiliferous rocks in ,colorado were deposited during the ,cambrian ,period1 at a time when over much of the world the seas were creeping in across wide1 level plains formed during the ,lipalian ,interval4 ,colorado was not covered by these seas until quite late in the ,cambrian ,period4 ,beach deposits progressively younger in age suggest that the sea invaded from the west1 and spread slowly eastward1 inundating most of the central part of the state but not the extreme north or south4 ,the beach deposits1 now called the ,sawatch ,sandstone because they are well exposed in the ,sawatch ,range1 are composed mostly of fine quartz sand4 ,they are colored with glauconite1 a green mineral1 and hematite1 a dark red mineral1 so that the rock has a variegated appearance4 ,the post office at ,manitou is built of this red and green rock1 and good exposures of it exist in ,williams ,canyon near ,manitou1 along ,u4 ,s4 ,highway #bd northwest of ,manitou1 near ,red ,cliff and ,minturn1 and in ,glenwood ,canyon4 ,the sea which crept over ,colorado at this time contained small conical-shelled mollusks1 brachiopods1 and trilobites4 ,their shells can occasionally be found in ,cambrian rocks in ,williams ,canyon and in the ,sawatch and ,mosquito ,ranges4 ,at two localities unusual fossils called graptolites have been found in thin ,upper ,cambrian shales overlying the ,sawatch ,sandstone4 ,illustration3 ,these fossils can occasionally be found in ,cambrian rocks in central ,colorado4 ,ordovician ,period 7#ddj-ejj million years ago7 ,the sea deepened and widened as the ,ordovician ,period began1 and a series of limestones and dolomites was deposited1 either on top of the ,sawatch ,sandstone or1 where the ,sawatch had not been deposited1 directly on the ,precambrian4 ,these rocks are now called the ,manitou ,formation4 ,the fossils in these rocks are much more varied than those in the ,sawatch ,sandstone3 snails1 echinoderms1 sponges1 cephalopods1 brachiopods1 and trilobites are common4 ,the ,ordovician sea must have teemed with life1 as many rocks deposited at this time are more than half composed of animal remains4 ,in addition to hard-shelled animals which formed fossils1 there were probably abundant soft-bodied animals such as jellyfish and worms1 which left no record of their presence4 ,after deposition of the ,manitou ,formation1 the seas receded slightly4 ,a new series of sands was deposited above the ,manitou in central ,colorado4 ,these now form the ,harding ,sandstone1 a formation of unusual interest because it contains remains of the earth's earliest known vertebrates1 primitive jawless fish called ,agnathids4 ,in places in the ,harding ,sandstone there are dense accumulations of the tiny polygonal armor plates from these fish4 ,although no whole fish have been found1 we can reconstruct their appearance by comparing individual plates or groups of plates with later1 better known relatives4 ,also present in great quantities in the ,harding ,sandstone are conodonts1 peculiar tiny brown tooth-like fossils4 ,relationships of the conodonts are unknown2 they may be parts of the ,agnathids1 or perhaps they represent some entirely different group of animals1 with no living relatives4 ,after deposition of the sands of the ,harding ,sandstone1 the sea deepened locally and the ,fremont ,limestone1 a massive gray crystalline limestone containing many marine fossils1 was deposited4 ,mollusks 7some quite large71 brachiopods1 and corals contributed their shells to the ,fremont ,limestone4 ,the chain coral ,catenipora and the horn coral ,streptelasma may often be used to identify the formation4 ,the ,fremont ,limestone was deposited very late in the ,ordovician ,period4 ,probably the seas were much more extensive then than present deposits indicate2 subsequent erosion has at several times erased the evidence in uplifted areas4 ,illustration3 ,these ,ordovician fossils can be found in the ,manitou ,formation in the ,colorado ,springs area4 ,illustration3 ,the earliest known fish remains come from the ,ordovician ,harding ,sandstone of central ,colorado4 ,these fragments of the protective plates have been magnified about five times4 ,illustration3 ,corals and coral-like organisms occur in the ,ordovician ,fremont ,limestone4 ,silurian ,period 7#djj-ddj million years ago7 ,until very recently1 no ,silurian rocks or fossils were known in ,colorado1 and it was thought that seas did not extend into the state during this period4 ,however1 a few years ago good ,silurian corals and brachiopods were discovered near the northern edge of the state4 ,they occur in broken blocks and patches of ,silurian limestone1 mingled with blocks of other sedimentary rocks and1 oddly enough1 with volcanic material4 ,what seems to have happened here is that sedimentary layers of ,silurian age were present over northern ,colorado at one time4 ,during some subsequent period of volcanism1 volcanic lavas penetrated these sediments from below4 ,near the volcanic tubes1 broken1 angular fragments of the surrounding sedimentary rocks were sometimes carried upward or downward by the motion of the lava4 ,much later1 both the volcanic outpourings 7if the lavas ever reached the surface7 and the sediments were stripped away by erosion1 probably at a time when mountains were rising in the area4 ,only the deep portions of the tubes that fed the volcanoes were preserved4 ,these tubes are called diatremes1 and thanks to the blocks of sedimentary rock in them we know that there were indeed seas in ,colorado during ,silurian time1 seas containing the abundant life of a shallow marine environment very much like that existing at the same time in ,illinois1 ,iowa1 and ,indiana4 ,devonian ,period 7#cej-djj million years ago7 ,as far as we know now1 ,colorado was just a little above sea level during most of ,devonian time4 ,early and ,middle ,devonian deposits are lacking4 ,late in the period1 however1 ,colorado was widely inundated once more4 ,embayments of a western sea covered most of the central part of the state and an area in southwestern ,colorado around ,ouray4 ,deposits formed in these embayments have been given several names4 ,chaffee ,formation is the name most commonly used in central ,colorado2 ,ouray ,formation identifies rocks of the same age in southwest ,colorado4 ,the ,chaffee ,formation has been subdivided into two well defined units1 the ,parting ,sandstone or ,quartzite1 and the ,dyer ,dolomite or ,limestone4 ,many ore deposits are associated with these rock units--notably deposits of lead and zinc4 ,the ,parting ,sandstone is frequently so well cemented with silica that it is actually a quartzite2 thin shale beds or 8partings0 make it easy to recognize4 ,it frequently contains remains of fossil fish and distinctive beds of algae4 ,the ,dyer ,dolomite contains brachiopods and bryozoans1 mollusks and corals4 ,some of the best fossil hunting in ,colorado is in ,dyer beds around the ,white ,river ,plateau1 where the fossils frequently weather out of the rock as almost perfect specimens4 ,illustration3 ,these ,devonian brachiopods come from the ,white ,river ,plateau in western ,colorado4 ,mississippian ,period 7#caj-cej million years ago7 ,the sea continued to cover most of ,colorado after the end of the ,devonian ,period1 well into ,mississippian time4 ,mississippian rocks are characteristically thick1 massive gray limestones collectively called the ,leadville ,limestone4 ,this unit is well known as the host rock for many ,colorado ore deposits1 notably those around the town of ,leadville4 ,during ,mississippian time the western sea1 warm and rich in organisms1 covered much of ,north ,america4 ,brachiopods and corals flourished1 as did many other forms of life4 ,the seas during part of this time extended completely across ,colorado to merge with seas that covered the midwestern part of the ,united ,states4 ,over all this vast area1 as well as southwest into ,arizona1 the gray1 massive1 fossiliferous ,mississippian limestone is remarkably uniform and easily recognized1 although it is called by different names in different areas4 ,late in ,mississippian time1 the ,colorado area rose slightly and the sea in which the ,leadville ,limestone was deposited receded4 ,an interval of erosion followed4 ,the surface of the limestone was dissolved and pitted1 tunnels and caves formed where running water etched deep into the rock1 and a reddish soil formed on the surface and in the hollows4 ,this portion of the limestone1 which in some places also contains pebbles of chert1 is named the ,molas ,formation4 ,part of the ,molas may be ,pennsylvanian in age4 ,illustration3 ,mississippian fossils from western ,colorado show that seas covered much of the state about #ccj million years ago4 ,pennsylvanian ,period 7#bgj-caj million years ago7 ,as the ,pennsylvanian ,period began1 the ,colorado area continued to rise4 ,earliest deposits of this age are fine-grained black shales and sands--the ,glen ,eyrie ,formation along the southern ,front ,range and the ,belden ,formation in west central ,colorado4 ,then1 through millions of years1 mountain-building took place4 ,some areas rose more than others1 so that formerly flat-lying marine sediments were bent and broken1 and a series of high mountain ridges and deep basins were formed4 ,geologists sometimes call these the ,ancestral ,rocky ,mountains4 ,although the pattern of the mountains changed repeatedly1 the ,ancestral ,rockies consisted principally of two large ranges4 ,one range roughly paralleled the present ,front ,range1 but lay thirty to fifty miles further west4 ,the other extended from the ,san ,luis ,valley northwest toward ,colorado ,national ,monument1 including the area around the ,black ,canyon of the ,gunnison and the present ,uncompahgre ,plateau4 ,coarse sediments washed off both sides of both ranges1 and accumulated as alluvial fans and valley fill along the mountain margins4 ,these exist today as the ,fountain ,formation of the eastern ,front ,range1 the ,minturn ,formation between the ancient uplifts1 and the ,hermosa ,formation west of the western uplift4 ,illustration3 ,this paleogeographic map reflects the distribution of land and sea during the early part of the ,pennsylvanian ,period and shows where coarse sediments derived from the ,ancestral ,rockies were deposited4 ,,fountain ,,formation ,,minturn ,,formation ,,hermosa ,,formation ,illustration3 ,west of ,denver1 the main line of the ,denver ,rio ,grande ,railroad tunnels beneath steeply dipping sandstones and conglomerates of the ,fountain ,formation4 7,jack ,rathbone photo7 ,illustration3 ,corals1 brachiopods1 and fusulinid ,foraminifurida can be found in the ,pennsylvanian ,minturn ,formation at many places in the ,mountain and ,plateau ,provinces4 ,illustration3 ,in western ,colorado1 where vegetation is sparse1 rock structures are clearly defined4 ,this photograph shows beds of the ,pennsylvanian ,minturn ,formation sharply folded1 probably as a result of the deformation of gypsum in underlying layers4 7,jack ,rathbone photo7 ,in the ,flatirons near ,boulder1 ,red ,rocks ,park near ,denver1 and the ,garden of the ,gods near ,colorado ,springs we see well exposed examples of the ,fountain ,formation4 ,the ,minturn ,formation is visible along the ,eagle ,river west of ,wolcott1 and along ,gore ,creek near ,vail4 ,the ,hermosa ,formation forms striking red cliffs north of ,durango4 ,in the ,sangre de ,cristo ,mountains area1 exceptionally great and rapid deposition took place1 and the ,minturn ,formation is very thick4 ,in west central ,colorado1 near the towns of ,eagle and ,gypsum1 a large basin formed4 ,in it1 gypsum and other salts were deposited as arms of the sea were cut off from the main marine area4 ,the unusual appearance of the hills along the ,eagle ,river1 especially north of ,u4 ,s4 ,highway #bd1 is caused by the presence of gypsum in the bedrock4 ,in a similar manner1 the ,paradox ,basin was formed in southwestern ,colorado4 ,thousands of feet of gypsum1 salt1 and potash were deposited here1 probably also precipitated in restricted arms of the sea4 ,these minerals1 the so-called evaporites1 have since significantly controlled development of the landscape in ,gypsum ,valley and other parts of this region4 7,see ,the ,plateaus in ,chapter ,i and the section on ,gypsum in ,chapter ,,iii74 ,between the mountain masses and their surrounding alluvial deposits1 shallow seas repeatedly invaded the lowland areas of the state4 ,marine fossils in some parts of the ,minturn ,formation bear witness to as many as twenty marine cycles4 ,strangely1 the ,pennsylvanian ,period appears to have been cyclical in other parts of the ,united ,states as well1 for marine sediments are found alternating with nonmarine sediments in ,pennsylvania1 ,illinois1 ,kansas1 ,nebraska1 and ,new ,mexico4 ,in middle ,pennsylvanian time1 general uplift occurred in ,colorado1 and almost the entire state was above sea level for the rest of the period4 ,permian ,period 7#bbc-bgj million years ago7 ,by the end of the ,pennsylvanian ,period1 the mountains of the ,ancestral ,rockies had been almost entirely removed by erosion1 and the deep basins were filled with sediments4 ,colorado was once more a great plain1 sloping gently to the northeast4 ,in eastern ,colorado1 a shallow sea gradually dried up1 leaving some thin limestone and gypsum beds along its margin4 ,the western shore of this sea was edged with beaches and sand dunes1 preserved as the ,lyons ,sandstone4 ,the buildings of the ,university of ,colorado1 as well as many homes and other structures in the ,boulder-,denver area1 are faced with this beautiful salmon-colored sandstone4 ,illustration3 ,balanced ,rock1 in the ,garden of the ,gods northwest of ,colorado ,springs1 is an erosional remnant of iron-rich conglomerate and sandstone4 ,it remains while the rest of the surrounding layers are gone because it is harder and more completely cemented together by silica4 ,the rock is part of the ,late ,paleozoic ,fountain ,formation4 7,john ,chronic photo7 ,in the western part of the state1 ,permian deposits consist mostly of shales and sandstones4 ,the red color of these rocks1 and the complete absence of fossils in them1 suggest that the environment in which they were deposited was not marine1 but was a vast1 level mudflat subject to alternating wet and dry periods4 ,the shales and sandstones collectively are called the ,maroon ,formation1 named for ,maroon ,bells1 near ,aspen1 where they are dramatically exposed in the mountain cliffs4 ,illustration3 ,tracks of ,permian reptiles called ,laoporus coloradoensis occur in the ,lyons ,sandstone near ,lyons4 ,these are about life size4 ,during part of ,permian time1 a shallow sea extended from ,idaho1 ,utah1 and ,wyoming into the northwest corner of ,colorado4 ,in this sea was deposited the ,phosphoria ,formation1 a highly phosphatic limestone containing only rare1 poorly preserved molluscan fossils4 ,as the ,paleozoic ,era ended1 ,colorado was still flat and low-lying4 ,by this time land plants and animals had evolved1 but if vegetation grew in the ,colorado area1 or animals roamed it1 they left few fossil remains4 ,tracks of early reptiles have been found in the ,lyons ,sandstone4 ,dune sandstones here and in adjacent areas suggest that desert conditions may have prevailed1 in which case ,colorado would have been very similar1 scenically and climatically1 to ,sahara regions today4 ,illustration3 ,dark red ,pennsylvanian and ,permian conglomerates form the ,flatirons that overlook the ,university of ,colorado campus at ,boulder4 ,university buildings are faced with ,permian ,lyons ,sandstone quarried along the foothills of the northern ,front ,range4 7,university of ,colorado photo7 ,,mesozoic ,,era ,the ,mesozoic ,era1 popularly known as the ,age of ,reptiles or ,age of ,dinosaurs1 is divided into three periods4 ,the climate of the entire earth appears to have been warmer then than it is at present1 perhaps because of a different distribution of land and sea areas1 or because continental areas were not as high and mountainous as they are just now4 ,colorado was a rather low land area for most of the first two ,mesozoic periods2 then a vast sea covered the entire state for the remainder of the era4 ,illustration3 ,the pink cliffs of ,colorado ,national ,monument are made of ,wingate and ,entrada ,sandstones4 ,underlying them1 in the valley bottom1 ,chinle shales form steep red slopes4 7,william ,c4 ,bradley photo7 ,triassic ,period 7#ahj-bbe million years ago7 ,saharan conditions continued to prevail in western ,north ,america during the early part of the ,mesozoic ,era4 ,in central ,colorado1 the lowest ,mesozoic deposits are the ,triassic ,lykins ,formation1 a series of soft1 bright red sandstones and shales4 ,where the ,lykins is exposed along the ,front ,range1 its bright red color identifies it4 ,because of its softness1 it is often less prominent than adjacent rock layers in the mountain foothills4 ,the ,lykins ,formation includes some evaporites1 apparently derived from ,permian evaporites washed into the ,triassic ponds and lakes which existed occasionally in this region4 ,over almost the entire state1 the rocks deposited at this time are very similar4 ,formation names may differ--,lykins1 ,moenkopi1 ,chinle1 ,ankareh1 ,wingate--but the rocks are almost universally fine-grained sandstones and shales with a red or pink color4 ,they represent ancient coastal plain1 dune1 or delta deposits4 ,toward the western edge of the state they coarsen1 and contain layers of conglomerates similar to the ,triassic conglomerates of northern ,arizona and ,utah4 ,these suggest that mountain-building was taking place west of here at that time4 ,there are virtually no fossils known from ,triassic rocks in ,colorado1 although some fossil palm fronds have been found west of the ,san ,juan ,mountains1 in the southwestern corner of the state4 ,jurassic ,period 7#ace-ahj million years ago7 ,during the ,jurassic ,period1 ,colorado was still a low1 flat desert area with intermittent streams flowing eastward over the surface of older sediments4 ,the ,navajo ,sandstone1 formed from dune sands1 was deposited in the western part of the state4 ,streams flowing eastward from ,utah brought fine sediments--silts and muds--to western ,colorado1 forming what is now the ,carmel ,formation4 ,near ,canon ,city1 coarse gravels bear witness to local uplift in ,jurassic time4 ,both these gravels and the ,carmel ,formation were overlain by more dune sands1 now hardened into the ,entrada ,sandstone4 ,in ,late ,jurassic time the ,colorado area1 which had been predominantly desert since ,permian time1 appears finally to have been submerged once more4 ,fine calcareous muds of the ,curtis ,formation1 containing ammonites1 belemnites1 and other marine shellfish1 show us that a shallow sea transgressed from the west over the wind-blown sands4 ,this sea was1 geologically speaking1 of short duration--only a few million years4 ,bounded on almost all sides by desert1 it seems to have dried up1 depositing the gypsum that is now present in a thin layer along the ,front ,range between ,denver and ,canon ,city in the ,ralston ,formation4 ,at about this time1 however1 the climate underwent a major change4 ,deposits above the ,ralston indicate an increasingly moist environment1 the environment in which the ,morrison ,formation was deposited over most of ,colorado and parts of the adjacent states of ,kansas1 ,arizona1 ,utah1 and ,wyoming4 ,the ,morrison ,formation is exposed in many places1 and is characteristically composed of layers of fine1 limy mud1 brightly colored in streaks of red1 brown1 green1 and blue4 ,in most areas it is so soft that it becomes soil-covered2 it is well exposed only in roadcuts or where it is protected from erosion by a 8caprock0 of harder sediments or lava4 ,spectacular outcrops can be seen in new roadcuts along ,u4 ,s4 ,interstate highway #gj just west of ,denver4 ,illustration3 ,in this roadcut along ,u4 ,s4 ,interstate #gj west of ,denver1 ,jurassic and ,cretaceous rocks are unusually well exposed in the ,dakota hogback4 ,green and purple shales represent the dinosaur-bearing ,morrison ,formation4 ,the ,cretaceous ,dakota ,group forms the eastern1 higher half of the cut4 ,black layers are carbon-rich clays of the ,south ,platte ,formation1 frequently quarried locally for ceramic uses4 7,john ,chronic photo7 ,fossil dinosaur bones occur in great numbers in the ,morrison ,formation near the towns of ,morrison and ,canon ,city and at several other places in ,colorado4 ,those at ,canon ,city have been quarried extensively1 and are now mounted in a number of museums in the ,united ,states4 ,at ,dinosaur ,national ,monument1 in eastern ,utah and northwestern ,colorado1 many excellent remains have been found2 those in ,utah can be seen in place in the rock in a striking exhibit at the ,national ,monument4 ,illustration3 ,in an old painting1 a paleontologist contemplates fossil bones found near ,morrison4 ,the date is #ahgg4 ,the bones are those of the #gj-;foot dinosaur ,apatosaurus1 more commonly known as ,brontosaurus1 shown below in reconstruction4 ,illustration3 ,apatosaurus ,some of the dinosaurs known from the ,morrison ,formation reached #hj feet in length4 ,both plant-eating and meat-eating types are known4 ,in addition to the bones themselves1 gastroliths or gizzard stones can frequently be found2 these highly polished stones were as essential to dinosaur digestion as gravel is to a chicken or a caged canary4 ,along with the dinosaur fossils are found abundant remains of water plants called charophytes4 ,these plants formed tiny spiralled balls of calcite as part of their reproductive activities2 both the little balls and the stalks of the plants themselves occur in many parts of the state4 ,in western ,colorado1 near ,grand ,junction1 silicified shells of freshwater snails can also be found in the ,morrison4 ,early in the #aijjs vanadium1 radium1 and uranium were discovered in ,jurassic sandstones and mudstones of western ,colorado4 ,extensive mining in this area has revealed that these elements often become concentrated by groundwater in organic material such as fossil plant stems or dinosaur bones4 ,the search for radioactive minerals has thus brought to light many ancient fossil accumulations4 ,cretaceous ,period 7#gj-ace million years ago7 ,early in ,cretaceous time1 marine conditions once more prevailed in ,colorado4 ,this is indicated by a marked change in rock types from beach and near-shore deposits to true marine sediments4 ,illustration3 ,between the ,front ,range and the ,plains the ,cretaceous ,dakota ,formation forms a hogback ridge which can be traced for #bjj miles or more4 ,the well-cemented sandstone resists erosion1 and so remains as a ridge when softer layers are stripped away4 7,jack ,rathbone photo7 ,the sandstones derived from beach sands sometimes include coarse pebbles of chert which can be traced to sources in ,permian rocks of ,utah and ,nevada4 ,occasionally the beach and near-shore deposits include marine shells like oysters1 indicating that there were brackish and salt water lagoons and marshes along the shore4 ,the ,dakota ,formation represents the beach of the transgressive or advancing sea4 ,this formation contains oil in eastern ,colorado1 ,nebraska1 and ,wyoming2 the oil itself may have been derived from decay of organic materials in swamps behind the beaches and bars4 ,as the sea deepened in eastern ,colorado1 finer sediments were deposited4 ,these included the black muds of the ,benton ,shale1 and the ,niobrara ,limestone1 a shallow-water deposit containing abundant shells of clams 7,inoceramus and ,ostrea7 and ammonites and tiny one-celled animals called ,foraminiferida4 ,above the ,benton and ,niobrara ,formations lie the fine gray muds of the ,pierre ,shale4 ,several thousand feet thick1 the ,pierre contains occasional beautifully preserved ammonite shells as well as bones from fossil fish and swimming reptiles4 ,illustration3 ,cretaceous rocks in ,colorado are rich in fossil pelecypods4 ,each of the fossils illustrated above may grow to a much larger size than shown4 ,illustration3 ,shales of the ,laramie ,formation contain many recognizable plant fossils4 ,the rocks deposited in western ,colorado at this time are markedly different from those deposited in eastern ,colorado4 ,in the east1 deposits are fine and very limy1 containing abundant shells and little in the way of coarse debris4 ,in the west1 sandstones of the ,mesa ,verde ,formation dominate1 and coal beds suggest marshy or swampy conditions inshore from the ancient ocean4 ,this is just the pattern we would expect from a low-lying region bordering a shallow sea1 a region similar perhaps to the southeastern ,atlantic and ,gulf coasts of the ,united ,states today4 ,toward the end of the ,cretaceous ,period1 the sea receded from ,colorado4 ,beaches and bars of the retreating sea left a sandstone layer which now outcrops prominently east of the ,front ,range as the ,fox ,hills ,sandstone4 ,above lie interbedded sands and coals1 the ,laramie ,formation4 ,the presence of coal above beach sands shows that the coal swamps moved eastward as the sea retreated4 ,the exact age of the shoreline deposits and coal beds varies from place to place in such a way as to indicate that the sea withdrew slowly and irregularly4 ,in general the shore moved eastward1 but there are localities such as ,north ,park where deposition lasted much longer than elsewhere4 ,in some places no real beach was formed at the ancient strand line4 ,in western ,colorado1 the end of ,cretaceous time is marked by coarser beds1 indicating an increased rate of uplift in ,utah4 ,conglomerates were deposited in the beds of the ,mc,dermott ,formation1 now visible along the ,animas ,river south of ,durango4 ,,cenozoic ,,era ,it is characteristic of earth history that the younger the rocks are1 the more we know about them4 ,this is because younger rocks lie near the surface1 have not been disturbed as much by mountain building processes as have older rocks1 and have not been affected as strongly by repeated erosion4 ,many of the events of the ,cenozoic ,era are documented in detail in the geology of ,colorado1 and these events have intimately influenced the scenery as we see it today4 ,the ,cenozoic is the ,age of ,mammals4 ,how it happened that mammals triumphed over reptiles is one of the mysteries of geology4 ,some scientists think that climatic changes--dropping temperatures and increases in rainfall--swung the balance in favor of the warm-blooded mammals4 ,others believe that cosmic ray bombardment during some unusual astronomical event may have destroyed many surface-living dinosaurs1 while small burrowing mammals 7as well as many small reptiles7 were able to survive4 ,still others maintain that the superior intelligence and regulated body temperatures of mammals enabled them to win out in the battle for survival without the aid of climatic or cosmic change4 ,the names ,tertiary and ,quaternary1 used for the two ,cenozoic ,periods1 are holdovers from early studies in geology in which rocks were divided into ,primary 7very hard1 crystalline rocks such as igneous and metamorphic rocks71 ,secondary 7well consolidated layered rocks71 ,tertiary 7layered rocks which are not fully cemented but which are nevertheless fairly well consolidated71 and ,quaternary 7sediments in which the grains have not become cemented together74 ,tertiary ,period 7#c-gj million years ago7 ,during the first part of the ,tertiary ,period1 uplift began in earnest in ,colorado and adjacent states4 ,this uplift was part of the great ,laramide ,orogeny that built the ,rocky ,mountain chain from ,alaska to ,new ,mexico4 ,the entire area rose above the level of the sea1 and mountains were thrust up in a great series of north-south ranges that extended unbroken almost the length of the continent4 ,between the ranges1 thick layers of gravel and sand1 derived from the surrounding highlands1 were deposited in intermontane basins4 ,occasional freshwater limestones and shales indicate the presence of lakes4 ,in ,colorado1 many details of the formation of the ,rockies stand out in bold relief4 ,the ,front ,range moved upward sharply1 mostly as a linear block broken or faulted along both edges4 ,paleozoic and ,mesozoic sediments along the margins of the block were steeply tipped and in some places even overturned1 while in some localities ,precambrian rocks were thrust out over the younger sediments4 ,just east of the ,front ,range1 especially in the area around ,denver1 the land remained lower and was the site of thick deposits of gravel and sand eroded from the range4 ,the ,denver ,formation1 the ,arapahoe ,conglomerate1 and the ,dawson ,arkose are more than #b1jjj feet thick in this area4 ,these are delta and river sediments1 all varying a great deal from place to place4 ,individual layers of sand or gravel are not continuous over extensive areas1 but some1 such as the ,castle ,rock ,conglomerate1 are very prominent locally4 ,illustration3 ,on ,wolford ,mountain1 just north of ,kremmling1 ,precambrian granite lies on top of ,cretaceous shale4 ,the older rocks were thrust up and over younger rocks during the ,laramide ,orogeny4 ,the position of the fault shows clearly because trees prefer the granite soil above the fault to the shale below4 7,jack ,rathbone photo7 ,along the eastern margin of the ,front ,range west of ,castle ,rock and ,sedalia1 rocks deposited at this time are now folded steeply1 indicating that the mountains continued to rise even as basin sediments were being deposited4 ,in southern ,colorado1 the ,sangre de ,cristo and ,wet ,mountains were also formed as upthrust blocks4 ,between them1 the ,huerfano ,basin and adjoining ,raton ,basin received particularly rapid alluvial deposition4 ,in the ,raton ,basin1 quantities of vegetation were deposited in swamps and marshes1 forming the thick coal beds which can now be seen in road cuts west of ,trinidad and along the ,raton ,pass highway4 ,huerfano ,basin deposits contain some of the earliest known horse remains1 skeletons of a tiny four-toed horse called ,hyracotherium 7formerly known as ,eohippus74 ,illustration3 ,bones of ,hyracotherium1 the 8dawn horse10 have been found northwest of ,walsenburg in ,early ,tertiary sediments of the ,huerfano ,basin4 7,c4 ,r4 ,knight painting1 courtesy ,american ,museum of ,natural ,history7 ,other rising ranges provided material for alluvial deposition in ,north ,park1 ,middle ,park1 ,south ,park1 and the ,san ,luis ,valley4 ,layers of basalt and volcanic peaks show that as the mountains rose1 the crust cracked and allowed lava to rise to the surface in great quantities4 ,tertiary basalts are very much part of the ,colorado landscape3 some can be seen west of ,granby1 others in ,table ,mountains east of ,golden4 ,near ,boulder1 ,valmont ,dike was intruded1 though lava may not have reached the surface in that area4 ,spanish ,peaks in southern ,colorado1 ,mesa de ,maya1 the ,rabbit ,ears ,range1 ,grand and ,battlement ,mesas1 and many other volcanic features were formed at this time4 ,illustration3 ,the town of ,golden nestles between the ,front ,range and ,south ,table ,mountain4 ,tertiary basalt capping ,south ,table ,mountain covers beds of the ,denver ,formation4 ,it thins to the right1 or south1 indicating that its source was probably to the north or northwest4 ,buildings in the right foreground are the ,colorado ,school of ,mines4 7,jack ,rathbone photo7 ,illustration3 ,a series of almost vertical dikes radiate from ,west ,spanish ,peak4 ,surrounding sediments are ,tertiary4 ,weathering and erosion along sets of joints in the largest dike have shaped it into the 8,devil's ,staircase40 7,jack ,rathbone photo7 ,most of the rich mineral deposits of ,colorado are thought also to have been formed during the early part of the ,tertiary ,period4 ,solutions rich in gold1 silver1 zinc1 lead1 copper1 and sulfides of iron seeped into joints and faults in the crust as the mountains were pushed upward4 ,ore minerals crystallized out1 sometimes in veins in the ancient ,precambrian igneous and metamorphic rocks1 sometimes in ,paleozoic sediments4 ,these are further discussed in ,chapter ,,iii4 ,illustration3 ,the ,eocene ,green ,river ,formation includes great thicknesses of oil shale1 an untapped petroleum reserve containing perhaps three trillion barrels of oil4 ,the richest part of the oil shale is a dark brown layer called ,mahogany ,ledge1 visible here on cliffs just west of ,rifle4 ,if placed in a campfire1 fragments of this shale release enough oil to burn with a yellow1 smoky flame4 7,jack ,rathbone photo7 ,further to the north and west1 the ,uinta ,mountains rose4 ,they are a fault-block range1 but they lie at right angles to the general north-south trend of the ,rocky ,mountains4 ,south of them the ,uinta ,basin1 one of the largest of the intermontane basins1 received shaly deposits in a great lake which existed here for probably several million years4 ,the lake extended over some #ajj1jjj square miles1 and during its existence great quantities of tiny organisms lived in its waters4 ,oily material from these organisms was deposited in the mud of the lake sediments1 particularly in the eastern end of the basin1 there to remain trapped in a great oil-shale deposit4 ,fossil fish1 crayfish1 algae1 and many forms of insect and plant life have been found as fossils in these lake shales4 ,west of ,pikes ,peak1 another lake formed1 dammed by a lava flow from a nearby volcanic field4 ,fine volcanic ash falling into this lake preserved the trunks and leaves of many plants as well as abundant insects1 fish1 and occasional mammal bones4 ,these are now protected and exhibited in ,florissant ,fossil ,beds ,national ,monument4 ,the fossil plants1 among them redwoods1 poplar1 hackberry1 and pine1 suggest a climate warmer than the present one1 and have been taken to indicate that regional uplift to the present altitude had not yet occurred4 ,another rich deposit of fossil insects and plants occurs near ,creede4 ,other lake deposits in ,south ,park contain ash layers with fossil algae and snails4 ,illustration3 ,large petrified trunks of redwoods and other trees can be seen at ,florissant ,fossil ,beds ,national ,monument1 west of ,colorado ,springs4 7,john ,chronic photo7 ,in southwestern ,colorado1 extensive ,tertiary lava flows1 ash falls1 and river deposits form the eastern part of the ,san ,juan ,mountains1 the largest volcanic area in the state4 ,mineral collectors are attracted to this region by the many excellent localities for agate and other siliceous stones4 ,still another center of ,tertiary volcanism was located in what is now ,rocky ,mountain ,national ,park4 ,specimen ,mountain1 northwest of ,trail ,ridge1 was an active volcano about #cj million years ago1 shedding ash and lava over much of northern ,colorado4 ,the rhyolite which now caps the hill west of ,iceberg ,lake1 on ,trail ,ridge ,road1 was derived from this volcano1 but is now separated from it by the deep glaciated valley of the ,cache la ,poudre ,river and ,milner ,pass4 ,volcanic ash at times drifted far eastward and blanketed the surface of the plains1 burying specimens of many animals and plants4 ,the ,white ,river ,formation1 extending from northeast ,colorado northward into ,south ,dakota1 is formed of such drifting ash4 ,many now-extinct mammals have been excavated from this formation4 ,sometime after the mid-,tertiary episode of violent volcanic activity1 ,colorado was uplifted to its present altitude4 ,this was a general uplift1 raising the plains and plateau areas as well as the mountains4 ,the uplift was not an abrupt process1 but continued for perhaps ten million years4 ,it raised the entire state #c1jjj to #e1jjj feet above its previous level4 ,illustration3 ,pawnee ,buttes1 about #dj miles north of ,fort ,morgan1 rise like castles from the eastern ,prairie ,province4 ,remnants of ,oligocene and ,miocene sedimentary rock that once covered much of northeastern ,colorado and adjacent states1 they contain jaws1 teeth1 and other bones of primitive mammals4 7,department of ,highways photo7 ,during the remainder of the ,tertiary ,period1 ,colorado was the site of erosion rather than deposition4 ,however1 some stream material was deposited in the mountain valleys1 and on the prairies wind-blown and stream-borne sands were spread thinly1 interlayered with impure limestones deposited in ponds and lakes4 ,in the ,san ,luis ,valley1 deposition was probably more continuous than elsewhere1 as the exit from the valley was blocked by volcanic flows4 ,the deposits in this valley1 sands and clays of the ,santa ,fe and ,alamosa ,formations1 form a great artesian basin4 ,the rich agricultural development of the valley is made possible by water wells tapping these formations4 ,illustration3 ,remains of many now-extinct mammals have been found in ,tertiary sedimentary rocks of northeastern ,colorado1 in the general area of ,pawnee ,buttes4 ,those illustrated are ,oreodon from ,oligocene strata and a 8giraffe-camel0 7,oxydactylus7 from ,miocene rocks4 ,quaternary ,period 7#c million years ago to present7 ,the most significant feature of the ,quaternary ,period in ,colorado1 as elsewhere in the northern hemisphere1 is the evidence of glaciation4 ,during the first part of the ,quaternary ,period1 known as the ,pleistocene ,epoch1 great continental glaciers covered most of ,canada and much of northern ,united ,states4 ,the ice sheets did not extend southward as far as ,colorado1 but large valley glaciers developed in many of the mountain ranges of the state and left their traces in many mountain valleys4 ,illustration3 ,mills and ,jewel ,lakes1 in ,rocky ,mountain ,national ,park1 occupy small glacier-gouged basins in ,glacier ,gorge4 ,the flat-topped peak at the upper left is ,longs ,peak1 elevation #ad1bef feet2 ,pagoda ,mountain is in the center of the skyline4 ,bedrock in this area is ,precambrian granite1 gneiss1 and schist at the ,front ,range 8core40 7,jack ,rathbone photo7 ,the conditions leading to ,pleistocene glaciation are not fully understood4 ,climatic changes may have been initiated by a decrease in solar radiation1 changing patterns of ocean currents1 reduction of solar heating by volcanic dust1 or an increase in general elevation of the land4 ,as the climate became cooler and moister1 snowfall increased in the north and at high altitudes4 ,in areas where winter snowfall exceeded summer melting1 glaciers developed4 ,in ,colorado1 glaciers formed along the crests of the ,front ,range1 the ,sawatch ,range1 the ,elk ,mountains and ,west ,elk ,mountains1 the ,sangre de ,cristo and ,mosquito ,ranges1 the ,san ,juan ,mountains1 and the ,park and ,gore ,ranges4 ,glaciation in ,colorado was selective3 in many places elevation was sufficient for glaciation1 but snowfall apparently was not great enough4 ,where they did occur1 the glaciers extended down to elevations of about #h1jjj feet4 ,there1 temperatures became mild enough to melt the ice4 ,the mountain glaciers have left many tell-tale signs of their presence4 ,valleys above #h1jjj feet are ,u-shaped1 their upper ends bounded by horseshoe-shaped1 steep-walled cirques4 ,in the lower portions of the valleys1 at elevations just above #h1jjj feet1 lie long lines of glacial debris known as moraines3 terminal moraines forming crescents across the valleys to show where melting glaciers dropped their rocky loads2 lateral moraines along the sides of valleys2 medial moraines where glaciers from two valleys met4 ,terminal moraines1 often forming effective barriers across the present streams1 may act as dams1 creating lakes such as ,grand ,lake in ,rocky ,mountain ,national ,park4 ,there were at least three distinct glacial episodes in ,colorado4 ,this is known because careful studies of glacial debris in moraines reveal three different degrees of rock weathering4 ,all three stages can be seen in or near ,rocky ,mountain ,national ,park4 ,the oldest is represented by a moraine about three miles west of ,estes ,park1 where the ,big ,thompson ,river traverses a wide ,u-shaped valley before entering its narrow1 unglaciated canyon4 ,the next oldest is represented in terminal moraines further up the valley1 at ,aspenglen campground4 ,the youngest is shown in a prominent terminal moraine about one mile west of the park entrance in ,horseshoe ,park4 ,a large lateral moraine separates ,hidden ,valley from the south side of ,horseshoe ,park1 and an almost equally large lateral moraine is present on the north side of this valley4 ,at ,moraine ,park1 both sides of the valley are edged with lateral moraines also4 ,studies in ,rocky ,mountain ,national ,park have revealed many other details of glaciation in this area4 ,these are described in ,park ,service brochures and guidebooks1 in the museum at ,park headquarters1 and in informative roadside signs4 ,illustration3 ,a line of hikers approaches ,arapaho ,glacier1 west of ,boulder4 ,movement of the glacier is evidenced by the crevasses apparent just below the snowfield in the dirty gray glacial ice4 7,h4 ,h4 ,heuston photo7 ,several small glaciers are still present in the ,colorado mountains1 all in sheltered cirques above #aa1jjj feet4 ,these may be remnants of the former larger glaciers1 or new glaciers formed after a long warming episode4 ,a hike to one of these glaciers is a rewarding experience for anyone interested in geology4 ,some of the more accessible are ,st4 ,mary's ,glacier west of ,denver1 ,arapaho ,glacier west of ,boulder 7the ,boulder ,chamber of ,commerce sponsors a festive hike to ,arapaho ,glacier every ,august71 and ,tyndall ,glacier in ,rocky ,mountain ,national ,park4 ,the ,ice ,age brought drastic changes also to the landscape below #h1jjj feet elevation4 ,heavily loaded with glacial debris1 mountain streams disgorged coarse sands and gravels along the mountain front and in the intermontane basins4 ,as the glaciers melted after each period of expansion1 the swollen streams cut deeply into their former deposits and into much older rocks as well4 ,royal ,gorge1 the ,black ,canyon of the ,gunnison1 and many of the deep1 colorful canyons of the ,plateau ,province were cut or at least deepened by these waters4 ,the canyons along the east face of the mountains--,big ,thompson1 ,boulder1 ,clear ,creek1 and others--were also deepened and sharpened by the rushing ice-fed torrents4 ,on the prairies1 rivers dumping their loads of sand covered the older rocks4 ,sand dunes developed along the river channels4 ,bones and huge tusks of hairy mammoths were sometimes buried in these soft deposits2 now they are occasionally revealed as the dune and river sands are washed or blown away by continuing erosion4 ,about #bj1jjj years ago1 man arrived in ,colorado4 ,soon after this1 the water supply of the valleys diminished greatly1 and erosion slowed down correspondingly4 ,the climate gradually became semiarid to arid4 ,many features of the natural scene were much as they must have been a century ago1 without the highways1 dams1 and television aerials of today4 ,buffalo and many smaller types of game roamed the plains and foothills2 deer1 elk1 and bighorn sheep were plentiful in the mountains4 ,nomadic tribes camped and hunted in both mountain and prairie4 ,in the western part of the state1 homes could be built in the shelter of great caves1 as at ,mesa ,verde1 and game could be supplemented with corn and squash planted on plateau surfaces4 ,several features of ,colorado scenery changed with increasing aridity4 ,the glaciers of course were gone or nearly gone4 ,streams were no longer the violent torrents they had been4 ,many mountain lakes1 filled with sediment and vegetation1 became instead mountain meadows4 ,and the once fertile intermontane valleys became deserts4 ,illustration3 ,during the last ,ice ,age1 elephant-like mastodons roamed ,colorado4 ,as present-day erosion removes sediments1 bones1 teeth1 and tusks are frequently exposed1 especially in the ,prairie ,province4 7,c4 ,r4 ,knight painting1 courtesy ,american ,museum of ,natural ,history7 ,illustration3 ,mastodon ,on the eastern side of the ,san ,luis ,valley1 the ,great ,sand ,dunes developed at this time4 ,these dunes nestle against the ,sangre de ,cristo ,range1 where strong southwesterly winds blowing across the wide valley tend to funnel toward ,mosca and ,music ,passes4 ,these winds lift loads of sand from the lightly vegetated valley floor1 and drop it as they rise over the mountains4 ,where the sand is dropped1 the dunes have formed4 ,they rise to about #gjj feet above the valley floor1 and cover about forty square miles4 ,the low rainfall of the area1 seven to eight inches per year1 keeps vegetation from creeping over the dunes and makes them a most distinctive feature of ,colorado1 a lesson in geology in the making4 99 99 99 99 99 99 99 99 ,geologic processes in ,colorado now seem to be much reduced from what they were a few thousand years ago4 ,reduction in rainfall has led to reduced erosion4 ,mountain-building1 having reached a climax in ,tertiary time1 has declined markedly4 ,however1 we find evidence that volcanism has occurred within the last few thousand years and faulting within the last few hundred1 and ,colorado streams rise after sudden mountain storms to approximate the violent torrents of glacial times4 ,colorado's scenery1 fashioned during some three billion years of earth history1 is ever changing4 ,illustration3 ,the ,great ,sand ,dunes of ,colorado were formed during ,pleistocene and ,recent time by deposition of quartz sand lifted from unconsolidated alluvial deposits in the ,san ,luis ,valley4 ,the highest of the dunes rises #gjj feet above the adjacent valley floor4 7,john ,chronic photo7 ,,iii ,geology and ,man in ,colorado ,colorado's first permanent settlers arrived in #aheh1 when gold was discovered in river sands near what is now the city of ,denver4 ,the ensuing gold rush1 coming ten years after the rush to ,california1 rivalled it in fury and brought sudden wealth to lucky miners and the adventurous merchants who grubstaked them4 ,several hundred mining towns or 8camps0 sprang into existence almost overnight1 their sites determined by the geology of the mountain areas4 ,the cities of ,denver1 ,boulder1 and ,golden were established as milling and shipping centers for the products of the mines4 ,in #ahgf the now-wealthy area1 previously part of ,kansas ,territory1 became the ,state of ,colorado4 ,for more than a hundred years ,colorado's minerals--products of her long and diverse geologic history--have influenced her development in many ways4 ,the state's early wealth1 stemming from bonanzas in gold and silver1 is evidenced by palatial homes1 hotels1 and public buildings constructed during the first few decades of mining activity4 ,some of these are still standing--the opera houses at ,central ,city and ,aspen1 ,central ,city's famous ,teller ,house1 and the ,grand ,imperial ,hotel at ,silverton are examples4 ,many of the stories and legends of ,colorado's gold camps are recounted in ,stampede to ,timberline1 by ,muriel ,sibell ,wolle1 delightfully illustrated with sketches of old mining towns as they appear today4 ,mining in ,colorado1 published by the ,u4 ,s4 ,geological ,survey1 also makes fascinating reading1 as it contains many historical anecdotes and eyewitness accounts of gold-rush days4 ,development of the metal-mining areas in ,colorado followed a definite sequence4 ,placer gold was usually discovered first4 ,recovery of placer gold was followed by mining of gold from veins or 8lodes40 ,although at first only native gold was mined1 gold-bearing compounds such as telluride were soon recognized as an additional source1 especially at ,gold ,hill1 ,cripple ,creek1 and of course the camp that came to be known as ,telluride4 ,as gold sources were depleted1 silver1 first produced as a byproduct1 became of prime interest4 ,lead and zinc were in turn byproducts of silver mining4 ,other metals1 notably copper1 vanadium1 tungsten1 and iron1 were produced later4 ,molybdenum is the ,johnny-come-lately of the state's mining industry1 but is now the chief metal produced4 ,a uranium boom in the #aiejs brought a short rush to western ,colorado and new vigor to the economy4 ,oil was discovered near ,canon ,city in #ahfb4 ,the nearby ,florence field and a small1 shallow field near ,boulder preceded much greater discoveries in the ,denver ,basin1 the ,uinta ,basin1 and southwest ,colorado4 ,oil reservoirs1 confined to areas of sedimentary rock1 are found primarily in the ,prairie and ,plateau ,provinces of the state1 and recovery of the oil has done much to distribute population to these areas4 ,coal is also restricted to sedimentary rock areas4 ,coal production in ,colorado has waxed and waned with the years1 but has provided fuel for export1 for the railroads1 for the manufacture of electric power1 and for many of the state's industries4 ,a good picture of present mineral production in ,colorado can be obtained from the following summary for #aiga1 prepared by the ,colorado ,bureau of ,mines3 ,product ,value ,molybdenum #aje1chi1def ,petroleum #ij1did1dei ,sand and gravel #cb1hdb1ejc ,coal #cj1bea1ddc ,natural gas #ah1fie1bbe ,uranium #ah1jdh1fib ,vanadium #ae1hfc1eed ,cement #ac1cgg1ebj ,zinc #ac1caj1ghg ,lead #f1ehb1jbe ,tungsten #f1cfj1jbj ,limestone and dolomite #e1cig1egj ,silver #d1aih1jed ,fluorspar #c1hhg1baj ,copper #c1hge1igf ,stone #a1ifa1bgi ,gold #a1hcb1gia ,clay #ifb1ihf ,iron #hhj1jdg ,pumice #cji1cgj ,tin #bgh1hfb ,gypsum #bec1hef ,pyrites #adb1fdj ,all others #a1jia1ibg ,total 7#cgf1bhh1beb7 ,colorado is now the nation's leading producer of molybdenum1 tin1 and vanadium1 and second in output of tungsten4 ,in oil production it ranked twelfth among the states in #aifh1 but ninth in reserves1 with #dbj1jjj1jjj barrels of proven reserves on #a ,january #aifi4 ,an as yet untapped source of oil lies in the oil shales of western ,colorado4 ,as part of the natural environment1 water plays a major role in man's activities4 ,water problems in ,colorado revolve mainly around the best use of runoff in a state whose major catchment basins are across the continental divide from her largest population centers and most fertile farm land4 ,groundwater1 closely related to surface water distribution and movement1 is a geological problem1 and in ,colorado as in other states many government and private geologists serve farm and industrial communities in the search for usable supplies4 ,,caution3 ,old mines are dangerous6 ,they may contain water or deadly gases1 or be on the verge of collapse4 ,keep away from abandoned prospect pits and mine shafts4 ,,warn ,,and ,,watch ,,your ,,children4 ,,gold1 ,,silver1 ,,and ,,other ,,metals ,colorado's placer and lode sources of gold1 which gave first impetus to the series of mining booms in the state1 were fantastically rich4 ,summit and ,lake ,counties1 for instance1 each produced more than #e1jjj1jjj in placer gold between #ahei and #ahfg4 ,during the same nine-year period1 more than #i1jjj1jjj in lode gold was produced from ,gregory ,gulch1 a tiny canyon between ,central ,city and ,black ,hawk4 ,other districts rivalled or surpassed these figures4 ,early in the game it was recognized that almost all the deposits occurred along what came to be known as the 8mineral belt10 a fifty-mile-wide zone extending southwest from the ,boulder region4 ,most of the metals mined in the state come from this belt1 but there are three notable exceptions3 ,cripple ,creek1 ,silver ,cliff1 and western ,colorado vanadium and uranium districts4 ,in the first few years of the ,colorado rush1 gold ores and placer gold were discovered only in the northeastern part of the mineral belt4 ,gradually the belt was found to extend further and further southwest3 ,tincup was discovered in #ahfa1 ,silverton in #ahgj1 ,lake ,city in #ahga1 and ,telluride in #ahge4 ,aspen1 on the western edge of the belt1 was not discovered until #ahgi1 perhaps because the area was difficult of access and lacked the easily recognizable native gold4 ,in the northeast part of the mineral belt1 gold and other minerals occur in veins in ,precambrian granite and gneiss4 ,in the ,leadville and ,aspen areas1 ores are associated with altered ,paleozoic limestones4 ,at the southwest end of the mineral belt1 in the ,san ,juan ,mountains1 ore veins are found near or in ,tertiary volcanic rocks4 ,native gold1 gold-bearing compounds1 and other metallic ores in these veins originated where mineral-rich solutions from deep within the earth penetrated fissures and joints in the surrounding rock4 ,regardless of the age of the host rock1 almost all the ores of ,colorado were deposited in the early or middle ,tertiary ,period1 about #ce to #gj million years ago4 ,gold and silver are no longer mined extensively in ,colorado1 although any summer ,sunday will see weekend operators panning near mountain streams or trundling rock from one-man mines4 ,the recent rise in the price of silver has encouraged many miners to reopen old shafts4 ,the most active mines in the state today are those producing molybdenum1 lead1 zinc1 and vanadium4 7,vanadium1 although a metal1 usually occurs in ,colorado with radioactive minerals1 and so is discussed with them rather than with the metals47 ,illustration3 ,the ,colorado mineral belt extends from ,boulder ,county on the northeast to ,san ,juan ,county on the southwest4 ,almost all of the prominent mining districts in ,colorado lie along this belt4 ,cripple ,creek and ,silver ,cliff1 however1 lie far to the east of the general trend4 ,telluride ,denver ,colorado ,springs ,alamosa ,,boulder ,ward ,gold ,hill ,boulder ,nederland ,,gilpin ,central ,city ,black ,hawk ,,jefferson ,golden ,,clear ,,creek ,empire ,georgetown ,silver ,plume ,idaho ,springs ,,summit ,breckenridge ,,eagle ,,pitkin ,aspen ,,gunnison ,tincup ,,chaffee ,,park ,climax ,alma ,como ,fairplay ,,teller ,cripple ,creek ,,fremont ,,ouray ,ouray ,camp ,bird ,ironton ,,san ,,juan ,silverton ,,hinsdale ,lake ,city ,,la ,,plata ,durango ,,mineral ,creede ,,custer ,silver ,cliff ,all told1 some #dcj metal mining districts have been established as legal entities in the state of ,colorado4 ,each of these districts had the right to draw up its own regulations concerning prospecting1 claims1 and mining rights1 within a framework established by the ,federal government4 ,only a few of the districts ever became really significant producers4 ,the geology and history of several of the leading areas are presented in the pages that follow4 ,boulder ,county ,gold ,run1 near ,gold ,hill1 was the scene of one of the earliest strikes in ,colorado4 ,gold was found here in ,december #aheh1 and was sluiced from stream sands and mined from veins early in #ahei4 ,active placer mining lasted only about a year1 however1 and lode mining dropped off rapidly as near-surface oxidized ores were worked out4 ,when a smelter was erected at ,black ,hawk in #ahfh1 and sulfide ores could be treated1 there was a revival of activity4 ,in #ahfi the ,caribou and ,poorman mines near ,nederland were discovered2 they quickly became the most active mines in the county4 ,the ,ward district opened soon after4 ,in #ahgb1 a gold-silver telluride called petzite was found in veins at ,gold ,hill4 ,renewed prospecting in this area resulted in location of mines near ,sunshine1 ,salina1 and ,magnolia4 ,during the years that followed1 new mines appeared almost as fast as old ones were depleted4 ,in #ahib1 the peak year1 more than #a1jjj1jjj in gold and silver was produced2 total production has been about #be1jjj1jjj4 ,in #aijj1 a black mineral common in the ,nederland area was recognized as ferberite1 an ore of tungsten1 and a new rush to the area started4 ,during the next eighteen years ,boulder ,county was the main tungsten producer in the ,united ,states2 about #bd1jjj tons of tungsten trioxide1 worth #bc1jjj1jjj1 were produced here4 ,the ore was found in nearly vertical veins six inches to three feet thick1 in a lenticular area about nine miles long extending from ,nederland northeast to ,arkansas ,mountain1 four miles west of ,boulder4 ,boulder ,county is characterized by an abundance of small mines4 ,old shafts1 pits1 and mine buildings can be found throughout the central part of the county4 ,little mining is done here today2 many of the towns that once peppered these hills have fallen into decay or disappeared entirely4 ,central ,city and ,idaho ,springs ,the ,central ,city-,idaho ,springs area was the principal metal mining region in the state until the late #ahhjs4 ,in #aheh1 rich placer deposits were discovered in gravels and river terraces along both forks of ,clear ,creek4 ,exploration upstream led to discoveries of rich oxidized quartz veins at ,central ,city1 ,black ,hawk1 and ,idaho ,springs4 ,these veins1 which generally trend northeast-southwest1 extend through the mountains in a zone about six miles long and three miles wide between the two forks of ,clear ,creek4 ,the ores filled a multitude of cracks and fissures in the ,precambrian bedrock4 ,the veins are usually less than five feet thick1 and are almost vertical and often clustered in zones up to thirty feet wide4 ,the position of one of the vein systems may be seen clearly between ,black ,hawk and ,central ,city--the ore-bearing rock has been mined out1 but a series of collapsed tunnels marks the line where the veins crossed the valley4 ,a monument here commemorates the discovery of ,gregory ,gulch1 one of the richest localities in the state4 ,several rich veins were mined in both directions--southwest from ,central ,city and northeast from ,idaho ,springs--until the mines met4 ,the ,argo tunnel1 marked by dilapidated buildings and extensive dumps on the north side of ,idaho ,springs1 connected the two districts2 it was completed in #aijd4 ,the 8,patch10 a deep crater-like hole on ,quartz ,hill1 about one mile southwest of ,central ,city1 is an intriguing feature in this area4 ,it was produced by glory-holing1 a mining technique in which a deep tunnel is deliberately caved by blasting1 so that ores above the tunnel can be removed4 ,this glory hole was dynamited below an irregular mass of highly broken rock where many ore-rich veins converged4 ,after the caving1 ores were taken out through the remaining part of the tunnel4 ,the principal ore minerals of ,central ,city and ,idaho ,springs are native gold1 pyrite1 sphalerite1 galena1 chalcopyrite1 and tennantite4 ,prospecting for uranium was carried out during the #aiejs but no uranium was ever mined here4 ,the area has produced almost #bjj1jjj1jjj worth of gold1 silver1 lead1 zinc1 and copper4 ,a few mines still operate seasonally or on a small scale1 but tourists1 many of them riding ,jeeps across the mountainous terrain to visit mines and ghost towns1 are often more visibly active than the mines4 ,georgetown1 ,empire1 and ,silver ,plume ,a few miles southwest of ,idaho ,springs1 another mining area had a similar1 though less productive1 history4 ,in #ahei1 placer and lode gold were discovered near what is now ,georgetown4 ,placer mining dominated here between #ahei and #ahfc4 ,gravel and crushed rock from decomposed quartz and sulfide veins were washed through sluiceboxes in the same way as placer gravel1 gold being caught in riffles or gunny sacking on the bottoms of the troughs4 ,the veins were found to be decomposed to depths of about #dj feet2 below this the gold occurred closely associated with sulfides such as pyrite1 sphalerite1 galena1 and chalcopyrite1 from which it could not easily be separated4 ,however1 smelters were developed in #ahff for treatment of these sulfides1 and gold1 silver1 lead1 and copper were recovered4 ,gradually1 as the gold was worked out1 silver and lead became the important products of the mines4 ,illustration3 ,sluicebox mining was a common sight near the early gold camps1 where primary recovery was from placer deposits or decomposed quartz and sulfide veins4 7,state ,historical ,society of ,colorado photo7 ,leadville ,placer gold was discovered in #ahei in ,california ,gulch1 about seven miles north of the present town of ,leadville4 ,the rush that followed was short but sweet2 the camp was called ,oro--gold6 ,about #e1jjj1jjj was produced from the placer mines within two years1 though by #ahfa the area was all but deserted1 for the easily won placer gold was gone4 ,illustration3 ,early-day ,leadville sprawled among its mine dumps at an elevation of #aj1bjj feet4 ,the ,sawatch ,range1 in the background1 contained many smaller mining communities1 now deserted4 ,mt4 ,massive1 the state's second highest peak1 forms the crest of the continental divide here4 7,state ,historical ,society of ,colorado photo7 ,in #ahge a smelter was erected a few miles downstream from ,oro to process cerussite--silver-rich lead carbonate--that occurred in the placer sands4 ,for years this mineral had been considered a nuisance because1 being much heavier than sand1 it tended to separate out with the gold4 ,the new town of ,leadville sprang up near the smelter and shortly afterward more lode deposits were discovered south of the placer workings4 ,from #fc1jjj in #ahge1 production climbed to #b1ejj1jjj in #ahgh and more than #ae1jjj1jjj in the peak year of #ahhb4 ,geologically1 the ores of this district occur as ,tertiary replacements and veins in ,ordovician1 ,devonian1 and ,mississippian limestones4 ,the 8,blue0 or ,leadville ,limestone1 of ,mississippian age1 contains the richest ore4 ,ore deposits were formed after the limestones had been faulted and cracked extensively by mountain-building movements2 the ores themselves probably crystallized from molten or gaseous materials involved in related igneous intrusions4 ,river gravels and glacial debris mask the true nature of the lode deposits1 but studies in the mines show that the fault systems along which ores are deposited trend north or north-northeast4 ,the ,leadville district is now experiencing its third mining boom as a newly recognized lead-zinc orebody is being developed4 ,production is expected to reach #gjj tons of ore per day by #aiga4 ,total production of gold1 silver1 lead1 zinc1 and copper in the district has reached #ejj1jjj1jjj4 ,breckenridge ,breckenridge was also discovered in #ahei1 with placer gold the first attraction4 ,the placers gave out in #ahfb after about #c1jjj1jjj in gold had been recovered4 ,earliest attempts to mine the rich silver and lead veins of the district were in #ahfi4 ,as at ,leadville1 the sedimentary rocks of the area were intruded by granitic masses in ,tertiary time1 but here the sedimentary rocks are mostly ,pennsylvanian sandstones and shales4 ,these rocks were badly faulted and broken during the intrusion1 and the ores were deposited as the granitic material cooled4 ,the lode deposits occur mostly in small veins well hidden by surface sands and gravels4 ,some of the veins yielded exceptionally beautiful crystallized wire and flake gold1 specimens of which are on display at the ,colorado ,school of ,mines library in ,golden and in the ,denver ,museum of ,natural ,history4 ,dredging for alluvial gold was attempted in #ahih in the ,breckenridge district1 but this method of extracting gold was not successful until #aije4 ,a number of dredges operated between #aiaj and #aibe4 ,these floating behemoths shovel up gold-bearing gravels from the bottom and one side of the pond on which they float1 sort out the gold in giant sluiceboxes1 and spew out the leftover gravels in great arc-shaped heaps that can be seen near ,breckenridge and ,fairplay and in a number of other valleys in ,colorado4 ,they depend for their operation on a plentiful supply of water and a shallow water table1 but they can sift through quantities of gravel at relatively low cost4 ,all told1 about #g1jjj1jjj in gold has been dredged from this district4 ,fairplay ,illustration3 ,this gold dredge1 still floating in its pond just south of ,fairplay1 operated from #aida to #aieb4 ,with chains of buckets like those in the foreground1 it dug gravel #gj feet below water level1 carving a #ce-;foot bank above water level2 in effect it mined to a depth of #aje feet4 ,this dredge extracted nearly #aae1jjj ounces of gold from about #cc million cubic yards of gravel 7,john ,chronic photo7 ,another gold field discovered in #ahei was in the northwest corner of ,south ,park1 along the headwaters of the ,south ,platte ,river4 ,several mining camps were established here4 ,after early production of rich placer deposits1 claims were consolidated and large flumes constructed so that gold could be recovered by hydraulic mining4 ,in this type of mining1 streams of water from high-pressure hoses are directed at gravel surfaces4 ,the gravels are washed into long sluiceboxes1 where gold is caught in riffles4 ,hydraulic mining continued upstream from ,fairplay until about #aijj4 ,in #aibb a dredge was constructed near ,fairplay to process gravel along the ,south ,platte and in the valley floor4 ,an even larger dredge1 constructed in #aida1 operated until #aieb1 when rising labor costs overrode the narrow margin on which it operated4 ,at the time operations ceased1 the dredge was recovering about six cents in gold for each cubic yard of gravel processed4 ,placer gold has always been the principal mineral product of the ,fairplay area1 but native gold also occurs in the surrounding mountains in quartz veins1 and many small mines were developed to extract it4 ,sulfide ores were also mined2 they contained silver1 lead1 and zinc as well as gold4 ,in the ,mosquito ,pass and ,horseshoe ,amphitheater areas1 there is renewed activity now because of the recent rise in the price of silver4 ,silverton ,gold was discovered in the ,san ,juan ,mountains of southwest ,colorado in #ahgj4 ,the earliest mine1 near what is now ,silverton1 was located by a group of prospectors sent out by ,governor ,pile of ,new ,mexico ,territory4 ,since the site was on ,ute ,indian land1 real mining did not begin until a treaty allowing it was ratified in #ahgd4 ,production in the ,silverton district has been from veins in ,tertiary volcanic rocks within an elliptical area known as the ,silverton cauldron4 ,here the volcanic rocks1 part of the several thousand feet of lava flows and ash falls of the ,san ,juan volcanic field1 were cracked and faulted by a second period of igneous activity4 ,ores formed in the cracks and fissures4 ,in the #ahgjs the ,silverton district was very remote1 and difficulties with transportation retarded activity there4 ,in #ahhb1 however1 a narrow-gauge railroad was built connecting ,silverton with ,durango1 and the problem of transporting ore out of the isolated mountain valley was simplified4 ,the railway still exists2 a train makes daily passenger runs during the summer--the only remaining operating narrow-gauge line in the ,united ,states4 ,the track follows the ,animas ,river canyon1 whose cliffs and crags are dotted with long-abandoned mines1 prospect holes1 and mine buildings1 monuments to the tenacity and determination of the men who mined here4 ,production in this district was more than #bb1jjj1jjj in gold and #bj1jjj1jjj in silver between #ahgd and #aibc4 ,new activity is evident here1 as in other silver-rich areas of ,colorado1 because of recent demand for silver1 lead1 and zinc4 ,illustration3 ,silverton lies in a remote mountain valley in the ,san ,juan ,mountains4 ,silver1 gold1 lead1 and zinc have been mined here since #ahgd4 ,storm ,peak1 composed of ,tertiary volcanic rocks1 forms the backdrop2 the narrow-gauge railroad track is visible in the foreground4 7,jack ,rathbone photo7 ,ouray ,ouray was settled in #ahge1 when gold and silver deposits were found near ,mount ,sneffels4 ,since #ahgg1 mines in ,ouray ,county have produced over #ce1jjj1jjj in gold and #cb1jjj1jjj in silver4 ,the district is still quite active3 in #aife1 mines in this area produced more than #i1jjj1jjj in gold1 silver1 copper1 lead1 and zinc1 about a third of total ,colorado production of these metals for that year4 ,illustration3 ,a few miles south of ,ouray1 along ,uncompahgre ,gorge1 an old mine clings to the slope below the ,million ,dollar ,highway 7,u4 ,s4 #eej74 ,abrams ,mountain rises in the background4 ,the ,precambrian ,uncompahgre ,quartzite outcrops up to about the road level2 ,miocene ,sunshine ,peak ,rhyolite caps the peak4 7,jack ,rathbone photo7 ,a mile north of ,ouray a prominent intrusive stock marks the center of mining activity closest to ,ouray4 ,the richest deposits of the ,ouray area1 however1 lie about five miles southwest1 near ,mount ,sneffels and ,red ,mountain ,creek4 ,there1 several large mines1 including the famous ,camp ,bird mine1 have operated for many years1 extracting ore from hundreds of veins that underly the surface4 ,some of these veins are two to four miles long4 ,they are in ,tertiary volcanic rocks of the ,san ,juan ,formation4 ,quartz and calcite are the common gangue 7non-economic7 minerals1 and pyrite1 sphalerite1 galena1 and chalcopyrite are the most abundant ores4 ,most of the silver is in the galena2 gold occurs in streaks and nodules associated with quartz4 ,about ten miles south of ,ouray1 along the 8,million ,dollar ,highway0 7,u4 ,s4 #eej71 the ,red ,mountain district lies on the northwest edge of the ,silverton volcanic cauldron4 ,it contains a number of small pipelike bodies very rich in silver-copper and silver-lead ores4 ,following the mid-,tertiary volcanism and ore intrusion1 surface rocks in this area were intensely oxidized3 resulting iron oxides now form the gaudy reds and yellows of ,red ,mountain and the slopes near ,ironton4 ,this alteration1 as well as the fact that much of the area is covered with fallen rock1 stream gravels1 or glacial deposits1 compounds difficulties of locating the small though high-grade ore deposits4 ,the ,idarado ,mine1 on the east side of ,u4 ,s4 highway #eej near ,red ,mountain1 used to produce ores from nearby volcanic pipes2 now it produces from veins some distance to the northwest4 ,the area is honeycombed with tunnels and shafts4 ,aspen ,silver was found at ,castle ,creek and on ,aspen ,mountain in #ahgi4 ,a group of prospectors from ,leadville1 apparently after examining maps of the ,geological and ,geographical ,atlas of ,colorado published in #ahgg1 explored along the line of ,paleozoic limestones encircling the ,sawatch ,range4 ,as they had hoped1 they found ores similar to those at ,leadville in rocks of the same age4 ,mining began at ,aspen in #ahhj4 ,here1 as at ,leadville1 intrusion of granite porphyry into or near the ,leadville ,limestone had broken and deformed the layers1 and ores were deposited in fissures and as replacements during cooling of the intrusions4 ,the intricacy of faulting which controls the ore pockets in the limestone is well shown on the map of ,aspen ,mountain in ,chapter ,,ii4 ,glaciation occurred in this area1 and glacial deposits cover most of the ore bodies and outcrops so that little bedrock is exposed4 ,mapping was accomplished by extrapolating to the surface the bedrock patterns shown in mine pits1 shafts1 and tunnels4 ,aspen produced some of the richest silver ores in the world1 and thrived as a boom town for most of two decades4 ,in #ahhh the value of ores produced reached over #g1jjj1jjj2 the next year it topped #aj1jjj1jjj4 ,after the silver crash of #ahic production declined rapidly2 the last mines were closed in the #aibjs4 ,total production of silver1 lead1 zinc1 and copper reached about #ajj1jjj1jjj4 ,there was virtually no gold in the ores at ,aspen4 ,creede ,illustration3 ,creede and its mines are located in an area of ,tertiary rhyolite and dacite1 light-colored volcanic rocks4 ,happy ,thought ,mine ,amethyst ,mine ,west ,willow ,creek ,,amethyst ,,fault ,last ,chance ,mine ,del ,monte ,mine ,commodore ,mine ,jackpot ,mine ,coppervein ,mine ,bachelor ,mine ,,bulldog ,,mountain ,,fault ,kansas ,city ,star ,mine ,commodore ,tunnel ,mustang ,tunnel ,nelson ,tunnel ,exchequer ,mine ,,solomon ,,fault ,,campbell ,,mountain ,holy ,moses #b ,holy ,moses ,mine ,ridge ,mine ,solomon ,mine ,monte ,carlo ,mine ,mollie ,s4 ,mine ,east ,willow ,creek ,ramey ,tunnel ,dora ,belle ,mine ,mammoth ,tunnel ,homestake ,mine ,mammoth ,mine ,,mammoth ,,mountain ,nancy ,hanks ,mine ,pipe ,dream ,mine ,,the ,,narrows ,windy ,gulch ,,creede ,willow ,creek ,the ,creede district ranks as one of the most productive silver areas in the ,united ,states4 ,it came into being largely as a result of a discovery by ,n4,h4 ,creede in #ahhi4 ,when exploring in this area1 he was reported to have exclaimed 8,holy ,moses60 on examining a rich piece of ore1 thus giving the name to the mine which initiated the rapid development of the district4 ,by the end of #ahib the ,holy ,moses and nearby mines had produced ore valued at more than #d1jjj1jjj4 ,the area was so rich that it managed to survive #ahic's great decline in the price of silver2 by #aibj almost #db1jjj1jjj in gold1 silver1 lead1 and zinc had been mined there4 ,the ores1 silver-bearing galena1 sphalerite1 native gold1 pyrite1 and chalcopyrite1 are in quartz or amethyst veins in faulted and shattered ,tertiary volcanic rocks4 ,nearly all the ore deposits lie along a complex system of vertical faults1 the ,amethyst fault zone1 which runs more or less northwest-southeast through this region4 ,both the faulting and the enrichment of the fault fissures are believed to have taken place in mid-,tertiary time1 shortly after deposition of the volcanic host rocks4 ,cripple ,creek ,illustration3 ,cripple ,creek1 on the flanks of the ,pikes ,peak massif1 has produced more than #djj1jjj1jjj worth of gold4 ,the ,sangre de ,cristo ,mountains are visible in the distance beyond the ,arkansas ,river valley4 7,jack ,rathbone photo7 ,in #ahij1 two sheepherders stumbled on some richly mineralized rocks near ,cripple ,creek4 ,a boom developed immediately1 for the rocks contained both gold and silver4 ,since then1 the area has produced more than #b1jjj1jjj ounces of silver and nearly #ai1jjj1jjj ounces of gold4 ,cripple ,creek has produced almost half of all the state's gold and silver4 ,the ores are located in or at the edge of a large mass of middle ,tertiary volcanic rocks which form an elliptical basin or caldera several miles across4 ,the caldera1 surrounded by ,precambrian gneiss and granite of the ,pikes ,peak massif1 was probably formed by collapse of a volcanic center that had erupted through the older rock4 ,the collapse shattered the rocks around the basin margin1 and subsequent volcanic activity introduced mineral-rich solutions into the many faults and fissures produced by the collapse4 ,tellurides of gold1 silver1 and copper1 as well as pyrite1 sphalerite1 galena1 tetrahedrite1 and other minerals1 are characteristic4 ,climax ,illustration3 ,at ,climax1 the ore occurs scattered through the intrusive ,climax ,granite ,porphyry and the intruded ,idaho ,springs ,formation4 ,visitors can tour the surface workings during the summer months4 ,tertiary dikes ,shell of ,climax stock ,core of ,climax stock ,ore zone ,precambrian granite ,fault ,dykes ,molybdenum now ranks as the number one metal mined in ,colorado4 ,over #aje1jjj1jjj of 8moly0 was mined here during #aifi1 almost all of it from the ,climax ,mine1 the world's largest single source of this metal4 ,the ,climax deposit is located high on the west slope of ,ten ,mile ,range in central ,colorado1 about #ajj miles southwest of ,denver4 ,it is in the central part of the ,colorado mineral belt1 near the ,mosquito ,fault1 a prominent structural feature which extends about sixty miles along the north-south trend of the mountains4 ,rocks on both sides of this fault are intruded by ,tertiary granite dikes1 sills1 and stocks4 ,the ,climax ,mine is in a stock just east of the fault1 near the axis of a broad anticline in ,precambrian metamorphic rocks4 ,ore minerals at ,climax are molybdenite1 huebnerite1 and cassiterite2 pyrite is recovered also for the manufacture of sulfuric acid4 ,the ore is very low in metal content1 containing only one-third of a percent of molybdenum1 #j4jje tungsten trioxide1 and #j4jjja tin4 ,the great size of the ore body and efficient recovery by modern methods make ,climax a profitable mine1 however4 ,production has risen each year since the mine began operation4 ,urad ,mine near ,berthoud ,pass is a newly developed near-surface molybdenum mine similar to ,climax4 ,nearby at the ,henderson ,mine the ore body is more than half a mile below the surface of the ground4 ,,radium1 ,,uranium1 ,,and ,,vanadium ,over a large area of the ,plateau ,province in western ,colorado1 ,mesozoic sedimentary rocks are locally stained bright yellow1 orange1 or green4 ,such staining suggests mineralization1 and radioactive compounds were recognized here before #aijj4 ,at that time1 however1 there was little or no market for them or for the vanadium frequently associated with them4 ,when ,marie ,curie required radium for experiments with her newly discovered element1 the raw materials were sent from western ,colorado2 by and large1 though1 production of radium from these ores was prohibitively expensive4 ,in #aije1 vanadium was found to be effective in toughening steel4 ,the ,vanadium ,corporation of ,america was formed to mine the ,colorado ore4 ,this company mines a rich zone in the ,jurassic ,entrada ,sandstone1 where vanadinite occurs with carnotite and other uranium ores4 ,in the early days of vanadium mining1 the uranium ores were discarded with other gangue materials2 now1 of course1 uranium is produced from them4 ,since #aide1 uranium production has been an important ,colorado industry2 in #aifi about #ag1ejj1jjj worth was produced4 ,uranium occurs in the state in two very different situations4 ,in the ,plateau ,province1 where it was first discovered1 it occurs in sedimentary rocks as patches of pitchblende1 carnotite1 and a greenish yellow mineral called schroekingerite4 ,it is most abundant in the ,triassic ,chinle ,formation and the ,jurassic ,entrada and ,morrison ,formations1 where it was probably deposited by downward movement of rainwater from overlying uranium-rich ,tertiary volcanic rocks4 ,concentrations of uranium often occur in or near organic matter such as coal1 fossil bone1 or petrified wood1 so mines tend to be located along rock layers carrying abundant organic material4 ,another type of uranium ore is found in the ,mountain ,province4 ,veins in ,precambrian rocks of the ,front ,range and several other ranges contain pitchblende which seems to have been deposited by hot groundwater rising through broken and fissured ,precambrian rocks4 ,often exceedingly rich1 such ore is mined in the manner of most of ,colorado's metals4 ,the ,schwartzwalder ,mine1 a few miles northwest of ,golden1 has produced more ore of this type than any other mine in ,colorado4 ,,oil1 ,,natural ,,gas1 ,,and ,,oil ,,shale ,petroleum and natural gas have been found in large quantities in the ,prairie and ,plateau ,provinces in ,colorado1 as well as in smaller quantities in ,north ,park in the ,mountain ,province4 ,they generally occur in porous sandstone and limestone layers1 where they have been trapped by overlying finer-grained1 less permeable layers in or near folds and faults4 ,several oil and gas seeps were found along the mountain front shortly after the arrival of the earliest settlers4 ,near ,canon ,city1 on ,oil ,creek1 a plaque commemorates the first production3 ,oil ,creek--site of the first oil well in the west--second place in the ,united ,states to produce petroleum from wells4 ,in #ahfb 444 ,a4 ,m4 ,cassedy drilled an oil well #ej feet deep4 ,by ,february1 #ahfc1 production was one barrel a day4 ,later1 several thousand gallons of petroleum were produced by primitive methods1 and kerosene and lubricating oil were shipped by ox team as far as ,denver and ,santa ,fe4 ,about twenty miles to the southeast1 near ,florence1 the ,cretaceous ,pierre shales were drilled in #ahgf4 ,oil was found in a system of intersecting fractures and joints4 ,some of the early wells in the ,florence field are still producing1 making this ,colorado's oldest and longest producing field4 ,it has yielded more than #aj1jjj1jjj barrels of oil4 ,small quantities of oil have been produced near ,boulder since about #aijj1 also from ,pierre sandstones and shales4 ,in this area1 wells were located by 8dowsing0 or 8witching10 as was fashionable at the time4 ,several old rigs can be seen near ,boulder ,reservoir4 ,as at ,florence1 oil has been trapped in fractures of otherwise dense and impervious shale4 ,some gas is produced and is used by local farms4 ,more recently1 oil was found far beneath the surface in the northern part of the ,prairie ,province4 ,here1 in the ,denver ,basin1 oil is produced from several levels in the ,dakota ,sandstone4 ,the oil has accumulated in lenses of beach sand deposited along the shoreline of the ,cretaceous sea4 ,the general trend of the shoreline1 and of the oil fields1 is northeast-southwest4 ,the shore appears to have been similar to ,georgia's present coastline3 a swampy tidal zone separated from open sea by lagoons1 sandy bars1 and clean sand beaches4 ,individual oil pools in the ,denver ,basin are small1 but there are many of them2 they lie nearly a mile below the surface1 under much of ,morgan and ,logan ,counties and adjacent parts of ,nebraska4 ,exploratory and development drilling keeps total oil production at about #ej1jjj barrels a day4 ,oil and gas produced here is piped to ,denver and other ,colorado cities4 ,in southeastern ,colorado1 oil and gas occur in late ,paleozoic limestones and sandstones similar to those which outcrop at the edge of the ,wet ,mountains4 ,prospecting by geophysical methods and by drilling has revealed several small1 rich accumulations1 one of which is thought to contain about #cj1jjj1jjj barrels of oil4 ,the ,rangely field1 in northwestern ,colorado1 is the most productive field in the state4 ,located in the northeastern part of the ,uinta ,basin1 it is an outstanding example of an anticlinal field1 where oil is trapped in a large1 gentle dome4 ,the shape of the dome shows up well on the surface2 rock layers can be seen dipping outward in all directions from the town of ,rangely4 ,oil was found by drilling on the crest of the dome4 ,at first1 oil was produced from fractures in the ,cretaceous ,mancos ,shale at less than #a1jjj feet depth4 ,later1 deeper drilling showed that oil had also accumulated in the ,permian ,weber ,sandstone1 at #e1jjj to #g1jjj feet4 ,at present this field is producing about #bh1jjj barrels of oil a day1 but the figure is dropping each year as the field is depleted4 ,oil and gas are produced in southwestern ,colorado from the eastern edge of the ,paradox ,basin and the northern edge of the ,san ,juan ,basin4 ,in the ,paradox ,basin1 oil comes from ,pennsylvanian limestone mounds or reefs4 ,production in the ,colorado part of the basin has been at most a few thousand barrels per day2 more is produced in adjacent ,utah4 ,in the ,san ,juan ,basin1 gas and oil are trapped in thin porous layers of ,cretaceous and ,pennsylvanian sandstone1 between impervious layers of shale4 ,most of the production is in ,new ,mexico1 although some oil comes from the ,colorado part of the basin4 ,the greatest known potential oil resource in the world lies in the oil shales of western ,colorado4 ,the richest of these shales cover an area of #a1fjj square miles north of the ,colorado ,river1 south of the ,white ,river1 and just east of the ,colorado-,utah line4 ,the oil shales are part of the ,tertiary ,green ,river ,formation1 which extends over much of northwest ,colorado1 northeast ,utah1 and southern ,wyoming4 ,oily material called kerogen is locked in these rocks1 too solid to flow out of the fine pore spaces of the shale4 ,to free it the shale must be mined1 finely crushed1 and heated until the kerogen converts to liquid oil4 ,this is an expensive process1 and as yet production of petroleum from the oil shale has not been possible at a cost which will compete with production of oil and gas from wells4 ,the ,united ,states ,bureau of ,mines1 as well as a number of oil companies1 have sought for more than fifty years to discover a less expensive method for extracting oil from the shale4 ,no doubt at some time in the future a competitive technique will be developed1 or a growing shortage of other oil will bring world prices to a level with which present production techniques can compete4 ,oil and gas production in ,colorado is decreasing at present1 even though great efforts are being made to find new oil pools4 ,petroleum prospecting and wildcat drilling are carried out in as yet unproductive basins in the ,plateau ,province1 in intermontane basins such as the ,san ,luis ,valley1 and on the ,plains4 ,known reserves will continue to provide the state with significant income for many years to come1 and if oil shale recovery becomes profitable4 ,colorado's hydrocarbons will become the most prominent of her commodities4 ,,coal ,coal resources of ,colorado amount to about #fj billion tons4 ,only one per cent of this has been mined4 ,thousands of tons are now being produced daily from large mines in central1 southern1 and northwestern parts of the state4 ,colorado's coal deposits were formed during late ,cretaceous and early ,tertiary time1 when seas were receding from this region and the land was rising4 ,they represent accumulations of leaves and other plant material in swamps and flood plains similar to those now found in the delta of the ,mississippi ,river and in the swamps of southeastern ,united ,states4 ,almost all ,colorado coal is bituminous or soft coal4 ,coal was recognized early in ,colorado history by settlers along the mountain front1 and was mined west and north of ,denver in the #ahfjs4 ,several large underground mines still operate in this district1 supplying local power plants1 but production does not compare with that of the ,walsenburg-,trinidad area in southern ,colorado or the ,hayden area in northwest ,colorado4 ,the ,walsenburg-,trinidad region1 part of the ,raton coal field1 has produced coal since the building of the ,santa ,fe ,railroad in the early #ahgjs4 ,for many years coal from these mines moved the ,santa ,fe trains and many of the numerous smaller railroads that served ,colorado's cities and mining camps4 ,the location of the mines helped to determine the location of the ,colorado ,fuel and ,iron ,company smelter in ,pueblo4 ,now1 most southern ,colorado coal is used to produce electric power4 ,many small mines1 miles away from the power plant west of ,trinidad1 are deserted4 ,a large coal-burning power plant has recently been built between ,hayden and ,steamboat ,springs1 just west of the ,yampa ,river4 ,here1 some of the extensive coal deposits can be seen in road cuts along ,u4 ,s4 highway #dj4 ,until conversion to diesel fuel became almost universal in ,north ,american railroads1 mines of this district produced coal for locomotives4 ,in the heyday of the gold and silver mines1 coal was also mined near ,coalmont1 in ,north ,park1 and ,como1 in ,south ,park4 ,coal from these areas was used for fuel in nearby mining towns and ranches1 and for the narrow-gauge railroads that penetrated the mountains here4 ,at ,anthracite1 near ,crested ,butte1 high-grade anthracite coal was mined for a time4 ,identical in origin with other ,colorado coal1 the anthracite of this region was hardened by heat and pressures from ,tertiary igneous intrusions forcing their way into local sedimentary rocks during post-,cretaceous mountain building4 ,a multitude of other coal camps are scattered about ,colorado3 ,cokedale1 ,delcarbon1 ,coaldale1 ,roncarbo1 ,carbondale1 and ,cardiff stand out because of their suggestive names4 ,these early small camps are1 like their metal-mine cousins1 largely deserted today4 ,,construction ,,materials ,sand1 ,gravel1 and ,clay ,sand1 gravel1 and crushed rock rate high among geologic products in ,colorado2 more than #bg1jjj1jjj worth of these materials were produced in the state in #aifi4 ,highway and construction activities have brought recent expansion in the number and size of quarries and gravel pits4 ,increasingly1 ,coloradoans are insisting that quarries and pits be excavated only where they will not mar the natural beauty of the landscape1 and many old pits are now being filled in4 ,unfortunately1 the scars left by some quarries--such as that on the ,rampart ,range near ,colorado ,springs--are difficult to erase4 ,clay of good quality occurs in ,cretaceous deposits in many parts of ,colorado1 most frequently in the ,dakota or ,laramie ,formations4 ,in the area around ,golden1 the ,coors ,porcelain ,company for many years mined clay for use in pottery and low temperature ceramic ware4 ,scars from this mining can be seen along the mountain front north and south of ,golden1 and deep clefts within the town1 just west of ,colorado ,school of ,mines1 testify to the amounts of clay that have been removed4 ,colorado clay is not pure enough to be used in high temperature ceramics1 and the present use for it is in the manufacture of common tiles and bricks4 ,a recent development in ,colorado is the use of ,cretaceous ,pierre shales in manufacturing lightweight aggregate for building4 ,the shale is mined between ,golden and ,boulder1 near ,colorado highway #ic4 ,in the nearby plant1 it is pulverized and then heated in a large rotating cylinder until the surface of each particle fuses4 ,then the particles are quickly cooled4 ,the resulting product is much like cinder1 light in weight and yet strong4 ,it can be mixed with cement for use in construction work requiring a great strength-to-weight ratio1 or made into concrete blocks4 ,illustration3 ,quarrying of ,paleozoic limestones and dolomites along the east flank of the ,rampart ,range northwest of ,colorado ,springs has badly defaced a prominent mountain backdrop4 ,recent seeding efforts by quarry operators are returning the exhausted part of the quarry to its original lightly vegetated condition1 and hopefully1 as the quarry is depleted1 the scar will disappear4 7,john ,chronic photo7 ,stone ,in ,colorado1 as in most parts of the world1 building stone for local use is quarried locally4 ,two of the state's stones1 however--,yule ,marble from the ,crystal ,river ,canyon1 and ,lyons ,sandstone of the ,front ,range--have been more widely used4 ,the ,yule ,marble1 or ,yule ,colorado ,marble1 was produced by metamorphism of ,leadville ,limestone in an area intruded by the ,treasure ,mountain ,granite1 thirty-five miles south of ,glenwood ,springs4 ,this exquisite marble1 which has graced many famous monuments and buildings 7among them the ,lincoln ,memorial and the ,tomb of the ,unknown ,soldier71 is known for its almost uniform snowy whiteness and regular1 fine crystallization4 ,although its beauty1 massive character1 and uniformity made it a sought-after ornamental stone1 quarrying was economically marginal because of the remoteness of the site4 ,in spite of this1 nearly #g1jjj1jjj worth of the marble was produced before the quarry closed in #aidj4 ,illustration3 ,pure white marble was quarried for many years at the ,yule ,colorado ,marble ,quarry1 about three miles southeast of the village of ,marble4 7,u4 ,s4 ,geological ,survey photo7 ,the ,lyons area1 north of ,boulder1 provides pink1 hard1 even-grained sandstone which splits readily into slabs or flagstones4 ,these are used in the ,denver-,boulder area for sidewalks and patios as well as for facing buildings4 ,quarries owned by the ,university of ,colorado provide a constant supply of handsome facing material and flagstone for new university buildings1 although in recent years the high cost of stone construction has limited its use on the campus4 ,illustration3 ,lyons ,sandstone is quarried near ,lyons1 ,colorado4 ,the salmon-colored sandstone splits along surfaces defined by slight differences in size and arrangement of the sand grains4 7,john ,chronic photo7 ,illustration3 ,most of the buildings of the ,university of ,colorado are faced with ,permian ,lyons ,sandstone1 which is widely used for buildings and flagstones throughout the ,boulder-,denver area4 ,the ,university ,museum1 shown here1 was established in #aijb1 and contains over a million scientific specimens1 including many ,colorado fossils and minerals4 ,exhibits in the ,hall of ,earth portray ,colorado's geologic history4 7,tichnor ,bros4 photo7 ,the ,lyons ,sandstone was deposited as beach and bar sand along the edge of a sea which lay east of the ,front ,range in ,permian time4 ,after deposition1 the sand was deeply buried and compacted4 ,now tilted up along the ,front ,range uplift1 it comes to the surface along the east side of the range4 ,only between ,fort ,collins and ,boulder does the stone have the desirable combination of hardness1 thin-beddedness1 and color which makes it desirable for ornamental use4 ,the pink color of the ,lyons ,sandstone is derived from iron oxides1 mostly hematite1 disseminated between the sand grains4 ,dendrites 7often erroneously called fossil ferns or plants7 ornament some slabs2 they were formed by crystallization of manganese dioxide from groundwater as it slowly percolated through the rock4 ,lime and ,gypsum ,outcrops of the ,cretaceous ,greenhorn and ,niobrara ,limestones provide most of the cement materials in ,colorado4 ,a number of plants along the mountain front1 including a completely automated and dust-free one near ,lyons1 provide the major population centers with millions of tons of cement each year4 ,colorado is richly endowed with gypsum1 useful in cement and plaster manufacture and for ornamental stone and sculpture4 ,along the eastern front of the mountains1 gypsum occurs in the ,triassic ,lykins ,formation2 in the ,mountain ,province1 it is abundant in ,pennsylvanian sedimentary rocks4 ,particularly high-quality ,pennsylvanian gypsum is quarried at the town of ,gypsum1 west of ,eagle4 ,the ,colorado portion of the ,paradox ,basin1 in the ,plateau ,province1 contains immense deposits of ,pennsylvanian gypsum4 ,here1 rocks near the surface have been pushed up into sharp northwest-trending faulted anticlines by upward movements of gypsum and salt from depths of several thousands of feet4 ,the soluble salt and gypsum cores of these structures have been washed away more rapidly than the surrounding layers of sandstone and shale1 leaving depressions such as ,gypsum ,valley1 ,paradox ,valley1 and ,sinbad ,valley1 on the crests of the anticlines4 ,red and yellow ,triassic sandstones and shales1 especially the ,chinle ,formation and the ,wingate ,sandstone1 dip away from these valleys4 ,exploratory wells indicate that vast masses of salt and gypsum are present beneath the surface1 and may extend to depths greater than #aj1jjj feet4 ,,gems ,,and ,,ornamental ,,stones ,more than thirty different gems and ornamental stones are known to occur in ,colorado4 ,amazonstone1 amethyst1 garnet1 tourmaline1 aquamarine1 topaz1 lapis lazuli1 quartz crystal1 smoky and rose quartz1 sapphire1 several varieties of agate1 zircon1 and other attractive stones are gathered within the state1 mainly in the ,mountain ,province4 ,turquoise is known at several places in the volcanic area of southern ,colorado4 ,alabaster is mined along the northeastern mountain front near ,fort ,collins and ,loveland4 ,localities of interest to gem hunters are described in ,colorado ,gem ,trails and ,mineral ,guide1 by ,richard ,m4 ,pearl4 ,gem ,village1 in southwestern ,colorado on ,u4 ,s4 highway #afj between ,durango and ,pagosa ,springs1 is a favorite stopping place for tourists wishing to see or buy colorful and attractive ,colorado stones such as petrified wood1 agatized dinosaur bones1 chalcedony1 and jasper4 ,,water ,although not all aspects of water and water supply are geologic1 water is an important geologic agent1 determining the shape of the surface1 the distribution of minerals1 and the location of caves4 ,water used in ,colorado comes entirely from precipitation within the state1 as all of ,colorado's rivers flow from ,colorado outward toward the surrounding lower-elevation states4 ,surface ,water ,illustration3 ,a cross section through the ,front ,range northwest of ,denver shows the redistribution and use of western slope water in eastern ,colorado through the ,colorado-,big ,thompson ,project4 ,this project has cost about #afj1jjj1jjj1 but it is repaying the investment many times over by providing electric power and increasing farm production4 ,moisture carried by prevailing westerly or northwesterly winds falls primarily on ,colorado's western slope1 although at some times of year precipitation may come from the northeast or southeast4 ,west of the continental divide1 where population is sparse1 there is a surplus of water4 ,east of the divide1 where more than #ij per cent of the population lives1 water is in desperately short supply4 ,the high and largely unpopulated ,mountain ,province receives by far the greatest proportion of precipitation1 while agricultural areas of the ,prairie and ,plateau ,provinces receive much less4 ,needless to say1 the major problem involving water in ,colorado is how to move it from areas where it is abundant to areas where it is needed4 ,in many parts of the state1 complex water laws and complicated irrigation canals and water systems were developed soon after the area became settled4 ,gradually but inevitably1 water resources have been transferred from the western slope to the eastern4 ,however1 such transfer must be undertaken with due regard for the rights of downstream users1 notably ,california1 ,arizona1 and ,new ,mexico4 ,one of the largest water movement schemes in the state is the ,colorado-,big ,thompson ,project4 ,water that otherwise would flow into the ,colorado ,river is piped from ,grand ,lake through the ,alva ,b4 ,adams tunnel under the high mountains of ,rocky ,mountain ,national ,park1 and into the ,big ,thompson drainage near ,estes ,park4 ,it then travels through a series of reservoirs and tunnels into the ,south ,platte ,river basin1 where it is used for irrigation and household water4 ,the water is pumped up the western gradient of this system by electric power produced as it flows down the eastern slope4 ,surplus electric power serves the ,colorado-,wyoming area4 ,another large project is the ,denver ,water ,board's ,dillon ,reservoir ,project1 in which western slope water collected at ,dillon is pumped twenty-three miles under the continental divide through the ,harold ,d4 ,roberts tunnel to the ,north ,fork of the ,south ,platte ,river for use by the city of ,denver4 ,the exit point of this tunnel can be seen a few miles west of ,grant along ,u4 ,s4 highway #bhe4 ,this project is continuously growing as ,denver's water needs mount4 ,in each of these projects1 engineering geologists played a prominent part in locating dams and tunnels that would not leak or fail1 and that could collect and transport a maximum amount of water during the high-runoff spring season for distribution through the rest of the year4 ,fortunately for geologists1 the tunnels and bores necessary to the projects allowed them to learn a great deal about the structure of the interior of the high mountains1 and helped to improve their interpretation of earth history in this most interesting region4 ,the necessity for storing irrigation water along the eastern mountain front has led to the creation of hundreds of new lakes in the region4 ,although water levels vary with the season1 many of the lakes provide opportunities for water sports and recreation for the burgeoning inland population4 ,two large dams have recently been built in western ,colorado for another purpose3 to control the flow of water in the ,colorado ,river drainage basin4 ,electric power for western ,colorado also comes from these dams4 ,one of the dams is on the ,gunnison ,river at ,curecanti1 upstream from the ,black ,canyon of the ,gunnison ,national ,monument1 and the other is on the ,frying ,pan ,river near ,ruedi4 ,the latter was completed over the objections of geologists1 who believed that the extensive gypsum deposits underlying the damsite would cause its failure4 ,cement pumped deep into the rocks in the vicinity has so far prevented serious rupture4 ,there is strong resistance by conservation groups to the construction of more dams on ,colorado ,river drainage1 primarily because the ,colorado and its tributaries pass through many irreplaceable canyons1 some of them parts of ,national ,parks and ,monuments1 that are very much a part of our western heritage4 ,groundwater ,illustration3 ,in the ,san ,luis ,valley1 runoff from the ,san ,juan and ,sangre de ,cristo ,mountains sinks into layers of sand in the ,alamosa ,formation4 ,flowing along the sand layers toward the center of the valley1 it provides artesian water for irrigation of valley farmlands4 ,,san ,,juan ,,mountains ,,limit ,,of ,,flowing ,,wells ,,hubbard',s ,,well ,,ottoway',s ,,well ,,alamosa ,,well ,,george ,,newsom',s ,,well ,,calkin',s ,,well ,,limit ,,of ,,flowing ,,wells ,moraine ,alluvial ,slope ,,sangre ,,de ,,cristo ,,mountains ,sands1 lava beds1 gravels1 conglomerates1 etc4 ,alamosa formation ,granites ,,west ,,sante ,,fe ,,formation ,,sante ,,fe ,,formation ,,east ,groundwater is extremely important to ,colorado1 especially in the ,prairie ,province and the ,san ,luis ,valley4 ,below these two areas lie a number of distinct and productive groundwater aquifers1 several of them artesian4 ,in ,otero ,county1 for example1 there are five major aquifers3 three separate ,quaternary gravel deposits1 the ,cretaceous ,dakota ,sandstone1 and the ,cheyenne ,sandstone ,member of the ,purgatoire ,formation1 also ,cretaceous4 ,all these aquifers are characterized by their high porosity and permeability1 which allow water to flow rapidly through them4 ,wells in the younger1 shallower aquifers produce as much as #b1jjj gallons per minute2 those in the older1 deeper aquifers produce about eighty gallons per minute1 some of it with an artesian 8head40 ,the ,san ,luis ,valley supports intensive agriculture1 made possible by a great artesian water supply4 ,a thick series of soft interlayered clays and sands1 the ,alamosa ,formation1 slopes down toward the center of the basin from the surrounding mountains4 ,water entering the sandstone beds at the mountain edges flows through the sand layers held there by the impermeable clay beds4 ,by the time it reaches the center of the valley1 it has developed considerable hydrostatic head1 and the water rises in wells without pumping4 ,unfortunately1 both the irrigation water and the soils in the ,san ,luis ,valley are highly alkaline4 ,constant evaporation from the irrigated fields has concentrated the alkali near and on the surface1 rendering some of the land less usable than it was originally4 ,caves ,colorado has many caves1 most of them carved by underground water in ,paleozoic limestone4 ,the ,cave of the ,winds at ,manitou is the only one in the state which has been developed as a tourist attraction4 ,it is in highly faulted ,ordovician and ,mississippian limestone near the mountain front1 where the faulting1 coupled with the high relief1 has accelerated solution of the rock by allowing groundwater to percolate downward rapidly4 ,the cavern was probably carved during the ,pleistocene ,ice ,age1 when surface water and groundwater were much more abundant than at present4 ,deposition of stalactites and stalagmites has occurred within the last few thousand years1 as supplies and movement of water have decreased4 ,spanish ,cave1 above timberline on ,marble ,mountain in the ,sangre de ,cristo ,range1 is probably the nation's highest limestone cave4 ,it is in thick folded and faulted ,pennsylvanian reef limestone1 at an elevation of over #ab1jjj feet4 ,the cave has many intricate passageways branching from its main vertical tubes and channels4 ,fulford ,cave1 south of ,eagle1 is in the ,mississippian ,leadville ,limestone of the northern part of the ,sawatch ,range4 ,many other caves are situated south of ,fulford1 near ,woods ,lake1 where the limestone is widely exposed and highly dissected4 ,fairy ,cave1 northeast of ,glenwood ,springs1 is the best known of the many caverns in the ,paleozoic limestones that form the southern flanks of the ,white ,river ,plateau4 ,illustration3 ,in ,cave of the ,winds near ,manitou1 ,paleozoic limestones1 cracked and tilted by uplift of the ,front ,range1 have been honeycombed by ground water4 ,calcite stalactites hang from the ceiling1 while stalagmites grow up from the floor4 7,cave of the ,winds ,company photo7 ,in the ,plateau ,province another type of cave is formed not so much by groundwater as by weathering of the flat-lying alternating beds of massive resistant sandstone and less resistant1 thinly bedded mudstone and shale4 ,where the resistant layers are undermined1 great arching caves develop4 ,these are best observed at ,mesa ,verde ,national ,park1 where many of them once sheltered ,indian communities4 ,they can also be seen in ,colorado ,national ,monument and along the ,colorado ,river and several of its major tributaries4 ,illustration3 ,along the edge at ,mesa ,verde1 caves in ,cretaceous ,mesa ,verde sandstone were used for shelter by ,indians4 ,springs near the bases of the caves1 which provided the ,indian communities with water1 probably contributed to the undermining of the sandstone cliffs4 7,colorado ,department of ,highways photo7 ,springs ,the multitudes of mineral and hot springs in ,colorado are a fascinating and interesting facet of the ,mountain ,province4 ,some are located along major faults1 where the rocks are so broken and shattered that groundwater can move freely toward the surface4 ,colorado ,springs1 ,manitou ,springs1 and ,eldorado ,springs are on the fault complex that forms the east edge of the ,front ,range4 ,glenwood1 ,juniper1 ,steamboat1 and ,poncha ,springs are on well defined faults also4 ,illustration3 ,glenwood ,hot ,springs flow from ,pennsylvanian shales of the ,belden ,formation1 where sedimentary layers are faulted by the sharp upward tilting against the south side of the ,white ,river ,plateau4 ,behind the hotel and on the right can be seen the ,mississippian ,leadville ,limestone1 cut by the ,colorado ,river4 7,from a painting by ,william ,h4 ,jackson1 courtesy of ,colorado ,state ,archives and ,public ,record7 ,many other springs do not seem to be controlled so strongly by faulting1 but owe their presence to sources of volcanic or magmatic heat which exist near to the surface of the ground4 ,some springs of this type issue from ,precambrian granite1 or ,cenozoic volcanic rock1 while others flow from sedimentary rock layers4 ,waunita ,hot ,springs and ,pagosa ,springs1 although near volcanic rocks1 reach the surface through porous sandstones and shales of ,cretaceous age4 ,mt4 ,princeton ,hot ,springs comes from alluvium but its heat source is the intrusive igneous rock which makes up part of the adjacent mountain4 ,springs of another general type are also present in ,colorado where aquifers1 generally sandstones1 are dissected by erosion4 ,these springs1 usually not highly mineralized or warm1 are most often found in the ,plateau ,province4 ,such springs are frequent at the bases of the great sandstone cliffs of ,mesa ,verde and ,colorado ,national ,monument4 ,manitou's carbonated springs1 which attract many tourists1 have their origin in the arrangement and nature of the rocks through which the water flows4 ,water from the ,pikes ,peak region1 slightly acid from its contact with the granitic rock1 flows into the ,manitou limestone all along ,ute ,pass fault1 which extends from ,cheyenne ,mountain northwest to ,woodland ,park4 ,descending through channels along the fault1 the water becomes pressurized4 ,because of its pressure and its acid content1 it partly dissolves the calcium carbonate of the limestone1 and from then on carries carbon dioxide in solution4 ,as the water comes to the surface at the low point of the fault exposure1 near the west edge of ,manitou1 the pressure is released and the carbon dioxide effervesces1 just as a bottle of soda water effervesces when the cap is removed4 ,,environmental ,,geology ,the preceding part of this chapter mentions many ways in which man's destiny in ,colorado has been shaped by geologic factors4 ,early ,coloradoans settled near gold and silver placers1 later ones near mines that produced ores of other metals1 or in the towns that sprang up around the mills and smelters that processed these ores4 ,our present distribution of population is partly a heritage from these first settlements1 partly a result of later discoveries of oil1 gas1 and radioactive minerals1 and partly a response to the state's extreme topographic variation1 which controls and delineates agricultural areas and transportation routes4 ,in recent years1 man has begun to appreciate the fact that he may benefit in other ways from knowledge about geology4 ,a new geology has developed--environmental geology--which may be defined as the total of all geological conditions and influences affecting the life and development of man4 ,environmental geology is a broad science1 concerned not only with the location of cities and towns1 but with the uses people make of the land and its economic products1 and with the relationship between the geological character of the land and the present and future location of roads1 dams1 bridges1 factories1 homes1 recreation facilities1 sanitary land fills1 and even sewage plants4 ,two aspects of environmental geology which are particularly pertinent to ,colorado's residents are discussed below4 ,landslides and slumping rock or earth are a frequent menace to ,colorado's development in the ,mountain ,province4 ,often activated by heavy rains or deep manmade cuts1 they can cause--and have caused--much damage to roads1 buildings1 and other works of man4 ,the flanks of ,north and ,south ,table ,mountains1 near ,golden1 are mantled by thick landslide debris2 intermittent movement of the individual slides has repeatedly affected the railroad1 irrigation ditches1 and roads4 ,as many as six different slides have moved within a single year4 ,in one slide area1 asphalt road material is estimated to be thirteen feet thick2 successive layers of pavement have been laid one on top of another to keep the street up to grade4 ,landslides and landslide-prone areas may not be obvious to the untrained eye4 ,each year buildings and roads are constructed on unsuitable rock and soil foundations1 in places where some degree of land slip is almost inevitable4 ,building in such areas is risky1 but sometimes worth the risk2 if condition are less than ideal1 risks can be reduced by specialized types of construction4 ,floods are a perennial threat to much of the state1 because of the high relief of the drainage basins and the torrential nature of the spring and summer rainfall4 ,their damaging effects were realized early in ,colorado's history1 when canyons were used as highways and railroad routes4 ,colorado's most expensive flood was probably the flood in the ,south ,platte ,river basin south of ,denver in #aife1 which caused #ejh1jjj1jjj worth of damage and drowned six people4 ,the losses can be attributed to man's failure to realize the significance of the ,south ,platte drainage routes and flood plains4 ,homes1 shopping centers1 and many other buildings occupied--and still occupy1 as of #aiga--land that has been intermittently flooded for many years4 ,the following description of this flood1 by ,h4 ,f4 ,matthai of the ,u4 ,s4 ,geological ,survey1 may help to convey some warning to residents or potential residents of the ,south ,platte valley and other river valleys in ,colorado3 8,the morning of ,june #af was most pleasant1 but conditions changed rapidly shortly before noon4 ,a tornado touched ground #ae miles south southeast of ,denver about #a p4m4 ,within the next hour1 another unroofed #cj homes in the little town of ,palmer ,lake1 #dj miles south of ,denver4 ,about #b p4m41 a dense mass of clouds descended and concealed the top of ,dawson ,butte1 #g miles southwest of ,castle ,rock2 and the little light remaining faded until it was dark black and frightening1 according to some people4 ,a nearby rancher's wife described the intense quiet as awesome1 but the calm did not last very long4 8,the deluge began1 not only near ,dawson ,butte1 but also at ,raspberry ,mountain1 #f miles to the south1 near ,larkspur4 ,the rain came down harder than any rain the local residents had ever seen1 and the temperature dropped rapidly until it was cold4 ,the quiet was shattered by the terrible roar of wind1 rain1 and rushing water4 ,then the thudding of huge boulders1 the snapping and tearing of trees1 and the grinding of cobbles and gravel increased the tumult4 ,the small natural channels on the steep slopes could not carry the runoff2 so water took shortcuts1 following the line of least resistance4 ,creeks overflowed1 roads became rivers1 and fields became lakes--all in a matter of minutes4 8,the flow from glutted ravines and from fields and hillsides soon reached ,east and ,west ,plum ,creeks4 ,the combined flow in these creeks have been described as awesome1 fantastic1 and unbelievable2 yet none of these superlatives seem adequate to describe what actually occurred4 ,large waves1 high velocities1 crosscurrents1 and eddies swept away trees1 houses1 bridges1 automobiles1 heavy construction equipment1 and livestock4 ,all sorts of debris and large volumes of sand and gravel were torn from the banks and beds of the streams and were dumped1 caught1 plastered1 or buried along the channel and flood plains downstream4 ,a local resident stated1 #8,the banks of the creek disappeared as if the land was made of sugar4' 8,the flood reached the ,south ,platte ,river and the urban areas of ,littleton1 ,englewood1 and ,denver about #h p4m4 ,here the rampaging waters picked up house trailers1 large butane storage tanks1 lumber1 and other flotsam and smashed them against bridges and structures near the river4 ,many of the partly plugged bridges could not withstand the added pressure and washed out4 ,other bridges held1 but they forced water over approach fills1 causing extensive erosion4 ,the flood plains carried and stored much of the flood water1 which inundated many homes1 businesses1 industries1 railroad yards1 highways1 and streets4 8,the flood peak passed through ,denver during the night1 and the immediate crisis was over by morning2 but those in the inundated areas were faced with a ,herculean task4 ,the light of day revealed the nature of the destruction--mud in every nook and cranny1 soggy merchandise1 warped bowling alleys1 drowned animals1 the loss of irreplaceable possessions1 to name a few types4 ,the colossal cleanup job1 which would take months1 began40 ,hydrogeological studies by the ,u4 ,s4 ,geological ,survey and ,corps of ,engineers give knowledgeable estimates of flood danger for different populated areas of the state1 and recommend that homes1 roads1 and other structures be placed above likely flood levels4 ,,glossary ,alluvial fan4 ,a cone-shaped mass of sediment built by rivers or streams as they issue from mountains onto more level ground4 ,alluvium4 ,stream deposits formed in recent geologic time1 composed of sand1 gravel1 and stones4 ,ammonite4 ,one of a large group of extinct mollusks related to the living chambered ,nautilus4 ,ammonite shells1 usually cone-shaped or coiled1 are divided into many chambers by crenellated septa4 ,angular unconformity4 ,a surface separating tilted or folded layers of rock from overlying less disturbed layers4 ,anticline4 ,an upward fold or elongated arch in rock layers4 ,aquifer4 ,a rock layer that is water-bearing4 ,artesian water4 ,groundwater that is under sufficient pressure to rise above the level at which it is encountered in a well4 ,it does not necessarily rise completely to the surface4 ,basalt4 ,an extrusive igneous rock1 fine-grained and dark colored1 composed mainly of calcium-rich feldspar and the black mineral pyroxene4 ,basement4 ,a name commonly applied to metamorphic or igneous rocks underlying the sedimentary rock layers4 ,batholith4 ,a large body of intrusive igneous rock1 #dj square miles or more in outcrop area1 which extends downward to an unknown depth4 ,bedrock4 ,the solid rock which underlies soil1 sand1 clay1 or other loose surface material4 ,belemnite4 ,the cigar-shaped internal shell of an extinct marine mollusk similar to a squid4 ,brachiopod4 ,one of a large group of marine shelled animals having two unequal1 bilaterally symmetrical shells4 ,bryozoa4 ,a large group of tiny colonial marine animals that secrete calcareous or horny coverings in a great variety of shapes4 ,caldera4 ,a large basin-shaped depression caused by explosion or collapse around a volcanic center4 ,cassiterite4 ,a heavy1 brown to brownish black mineral composed of tin and oxygen 7,sn,o7 that is an ore of tin4 ,cephalopod4 ,a marine mollusk with a head surrounded by tentacles4 ,squids and octupuses belong to this group1 as do fossil forms having straight or coiled shells divided into numerous interior chambers4 ,chalcopyrite4 ,a reddish-gold colored ore of copper 7,cu,fe,s74 ,cirque4 ,a deep1 steep-walled recess in a mountain1 caused by glacial erosion at the head of a valley4 ,concretion4 ,a nodular or irregular concentration of minerals such as calcite or limonite1 formed by precipitation of the mineral from groundwater around a nucleus4 ,conglomerate4 ,a rock containing coarse fragments of an older rock1 usually as rounded water-worn stones or pebbles4 ,conodont4 ,one of a group of tiny dark brown tooth-like fossils thought to be dermal or dental parts of some extinct group of fish4 ,diatreme4 ,a volcanic vent or pipe drilled through rocks by the explosive energy of gas-charged molten rock1 now containing igneous rock and often altered or unaltered fragments of the surrounding rock4 ,dike4 ,a vertical or nearly vertical sheet of igneous rock which cuts across the structure of adjacent rocks4 ,diorite4 ,an intrusive igneous rock composed of sodium-rich feldspar and dark minerals1 with only small amounts of quartz4 ,dip4 ,the angle at which a layer of rock is inclined below the horizontal4 ,dome4 ,a roughly circular upfold in which the rock layers dip outward in all directions from the center4 ,dowsing4 ,searching for underground water or ore with a divining rod1 usually a forked stick supposed to locate spots where the desired substance may be found under the surface4 ,echinoderm4 ,one of a large group of marine invertebrate animals1 most of which have pentagonal symmetry and a skeleton of many calcite plates4 ,many forms are spiny4 ,the group includes starfish and sea urchins4 ,evaporite4 ,chemical sediments precipitated when water 7usually sea water7 evaporates4 ,extrusive rocks4 ,igneous rocks formed when molten rock material is ejected onto the surface4 ,synonymous with volcanic rocks4 ,fault4 ,a break in the rocks in which there has been displacement of the two sides relative to each other4 ,fault block range4 ,a mountain range bounded on two or more sides by faults4 ,feldspar4 ,a group of light-colored aluminum silicate minerals that are major constituents of igneous rocks4 ,they contain potassium1 sodium1 and calcium in differing proportions4 ,fold4 ,a bend in rock layers4 ,foraminiferida4 ,one-celled marine animals with microscopic1 perforated1 many-chambered calcium carbonate shells1 often called forams4 ,fossil4 ,the remains or traces of an animal or plant which has been preserved in the rock4 ,fusulinid4 ,one-celled marine animals 7forams7 with shells which look like a grain of wheat in shape and size1 frequently abundant in ,colorado ,pennsylvanian rocks4 ,galena4 ,a heavy gray metallic mineral 7,pb,s71 often cubic in form1 that is the most important ore of lead4 ,gangue4 ,nonvaluable minerals occurring in veins with ore minerals4 ,glaciation4 ,alteration of the earth's surface by erosion and deposition by glacier ice4 ,glacier4 ,a body of ice originating on land by recrystallization of snow1 and showing evidence of movement by flowing4 ,gneiss4 ,a coarse-grained metamorphic rock usually banded with streaks of darker1 finer-grained rock4 ,granite4 ,an intrusive igneous rock consisting essentially of sodium or potassium feldspar and quartz1 often speckled with dark-colored minerals4 ,graptolite4 ,extinct marine organisms without known close living relatives1 with small black sawblade-like chitinous hard parts preserved as fossils4 ,hematite4 ,a steel gray or metallic grayish black or reddish gray mineral 7,fe,o7 that is an important ore of iron4 ,hogback4 ,a sharp-crested ridge formed by a resistant layer of steeply dipping rock4 ,huebnerite4 ,a heavy reddish brown mineral 7,mn,w,o7 that is a major ore of tungsten4 ,igneous rocks4 ,rocks formed by solidification from a molten state1 either at the surface 7extrusive7 or below the surface 7intrusive74 ,intrusive rocks4 ,igneous rocks formed when molten rock material solidifies without reaching the surface4 ,joint4 ,a fracture in the rock1 along which no discernible movement has taken place4 ,kerogen4 ,solid bituminous material in oil shales4 ,laccolith4 ,a lens-shaped mass of igneous rock intruded into layered rocks4 ,lava4 ,fluid or molten rock such as that which issues from a volcano4 ,lode4 ,a rock mass1 often a vein1 containing valuable minerals4 ,massif4 ,a mountainous mass that has relatively uniform geologic characteristics and which may embrace a number of peaks4 ,mesa4 ,a flat-topped mountain bounded on at least one side by a steep cliff4 ,metamorphic rock4 ,rock formed by alteration of pre-existing rock1 especially by great temperatures and pressures4 ,mollusk4 ,any one of the large group of invertebrate animals which includes the snails1 clams1 octopuses1 squids1 and their extinct relatives4 ,molybdenite4 ,a soft bluish gray1 metallic mineral 7,mo,s7 that is a major ore of molybdenum4 ,monocline4 ,a steplike fold in otherwise horizontal or gently dipping rock layers4 ,moraine4 ,an accumulation of unsorted rock material built up by the action of glacier ice4 ,native gold4 ,gold occurring in nature uncombined with other elements4 ,peneplain4 ,a land surface worn down by erosion to a nearly flat or broadly undulating plain4 ,petzite4 ,a heavy black or steel gray metallic telluride ore of gold and silver 7,ag,au,te74 ,placer4 ,a sand or gravel deposit containing particles or nuggets of gold or other heavy valuable minerals4 ,plateau4 ,an elevated1 comparatively flat surface of land1 usually larger than a mesa1 sometimes composed of many mesas1 and often dissected by deep stream valleys4 ,porphyry4 ,an igneous rock1 usually intrusive1 which contains conspicuous large crystals in a fine-grained matrix4 ,pyrite4 ,a brass-yellow metallic mineral 7,fe,s7 that is an important source of sulfur4 ,it is commonly known as fool's gold4 ,reef4 ,a moundlike limestone structure built in the sea by sedentary organisms such as corals4 ,rhyolite4 ,a light-colored volcanic rock with quartz and feldspar as the principal constituents4 ,schist4 ,a metamorphic rock characterized by parallel orientation of flat-grained minerals like mica4 ,sedimentary rocks4 ,rocks formed of fragments of other rock transported by wind or water1 or formed by precipitation from solution4 ,sphalerite4 ,an amber-yellow to black mineral 7,zn,s7 that is an important ore of zinc4 ,stalactite4 ,a cylindrical or conical deposit of calcite hanging from the roof of a cavern1 formed by evaporation of water droplets containing calcium carbonate4 ,stalagmite4 ,columns or ridges of calcite rising from the floor of a cavern1 formed by water containing calcium carbonate dripping from a stalactite4 ,stock4 ,a mass of igneous intrusive rock that covers less than #dj square miles1 has steep sides1 and extends to an unknown depth4 ,tennantite4 ,a metallic gray mineral that contains copper1 iron1 and arsenic1 and is an ore of copper4 ,tetrahedrite4 ,a brittle1 dark gray to black1 metallic mineral containing copper1 iron1 zinc1 and silver4 ,trilobite4 ,one of a primitive group of extinct marine crustaceans1 related to crabs and lobsters1 having segmented bodies divided by longitudinal grooves into three lobes4 ,unconformity4 ,a surface separating layers of rock1 formed by a period of nondeposition or erosion4 ,vein4 ,a crack or fissure filled with mineral material1 often with valuable ore minerals4 ,,suggested ,,reading ,there are thousands of scientific articles and books on ,colorado geology1 and many new ones appear each year4 ,following is a selection of books and booklets which we believe will be most useful and interesting in extending your knowledge of the state's geology4 ,donnell1 ,john ,r41 editor1 #aifj1 ,,geological ,,road ,,logs ,,of ,,colorado4 ,rocky ,mountain ,association of ,geologists1 ,denver4 ,itineraries for a number of geological trips along ,colorado highways and byways4 ,eckel1 ,edwin ,b41 #aifa1 ,,minerals ,,of ,,colorado1 ,a #ajj-,,year ,,record4 ,u4 ,s4 ,geological ,survey ,bulletin #aaad4 ,emmons1 ,s4 ,f41 ,cross1 ,whitman1 and ,eldridge1 ,g4 ,h41 #ahif1 ,,geology ,,of ,,the ,,denver ,,basin ,,in ,,colorado4 ,u4 ,s4 ,geological ,survey ,monograph #bg4 ,the classic early treatment of the surface geology around ,denver1 with many historic illustrations4 ,hansen1 ,wallace ,r41 #aife1 ,,the ,,black ,,canyon ,,of ,,the ,,gunnison ,,today ,,and ,,yesterday4 ,u4 ,s4 ,geological ,survey ,bulletin #aaia4 ,a readable account of this unusual national monument near ,montrose4 ,hansen1 ,wallace ,r41 #aifi1 ,,the ,,geologic ,,story ,,of ,,the ,,uinta ,,mountains4 ,u4 ,s4 ,geological ,survey ,bulletin #abia4 ,the eastern part of this range is in ,colorado4 ,henderson1 ,c4 ,w41 #aibf1 ,,mining ,,in ,,colorado1 ,a ,,history ,,of ,,discovery1 ,,development ,,and ,,production4 ,u4 ,s4 ,geological ,survey ,professional ,paper #ach4 ,lee1 ,w4 ,t41 #aiag1 ,,the ,,geologic ,,story ,,of ,,the ,,rocky ,,mountain ,,national ,,park1 ,,colorado4 ,u4 ,s4 ,national ,park ,service ,publication4 ,an old report1 not adequately superseded4 ,lovering1 ,t4 ,s41 and ,goddard1 ,e4 ,n41 #aiej1 ,,geology ,,and ,,ore ,,deposits ,,of ,,the ,,front ,,range1 ,,colorado4 ,u4 ,s4 ,geological ,survey ,professional ,paper #bbc4 ,a comprehensive study of mineral-bearing areas in the ,front ,range4 ,lohman1 ,s4 ,w41 #aife1 ,,the ,,geologic ,,story ,,of ,,colorado ,,national ,,monument4 ,colorado and ,black ,canyon ,natural ,history ,association1 ,grand ,junction4 ,pearl1 ,richard ,m41 #aief1 ,,nature ,,as ,,sculptor3 ,a ,,geologic ,,interpretation ,,of ,,colorado ,,scenery4 ,denver ,museum of ,natural ,history ,popular ,series ,no4 #f1 ,revised ,edition4 ,pearl1 ,richard ,m41 #aifi1 ,,exploring ,,rocks1 ,,minerals1 ,,fossils ,,in ,,colorado4 ,swallow ,press1 ,revised ,edition4 ,pearl1 ,richard ,m41 #aiga1 ,,colorado ,,gem ,,trails ,,and ,,mineral ,,guide4 ,swallow ,press1 #crd ,edition4 ,powell1 ,john ,wesley1 #ahgf1 ,,report ,,on ,,the ,,geology ,,of ,,the ,,eastern ,,portion ,,of ,,the ,,uinta ,,mountains ,,and ,a ,,region ,,of ,,country ,,adjacent ,,thereto4 ,u4 ,s4 ,geological and ,geographical ,survey of the ,territories4 ,one of the earliest accounts of geology in ,colorado1 written by the explorer of the ,colorado ,river and the father of the ,u4 ,s4 ,geological ,survey4 ,rabbit1 ,mary ,c41 and others1 #aifi1 ,,the ,,colorado ,,river ,,and ,,john ,,wesley ,,powell4 ,u4 ,s4 ,geological ,survey ,professional ,paper #ffi4 ,a resum of part of ,powell's work and a good discussion of the geologic history of the entire ,colorado ,river1 which begins near ,grand ,lake4 ,richmond1 ,gerald ,m41 #aife1 ,,glaciation ,,of ,,the ,,rocky ,,mountains4 ,a part of ,,the ,,quaternary ,,of ,,the ,,united ,,states1 ,princeton ,university ,press4 ,a summary of current knowledge of glaciation in ,colorado and surrounding areas4 ,rodeck1 ,hugo ,g41 editor1 #aifd1 ,,natural ,,history ,,of ,,the ,,boulder ,,area4 ,university of ,colorado ,museum ,leaflet ,no4 #ac4 ,contains articles on geology and biology4 ,untermann1 ,g4 ,e41 and ,untermann1 ,b4 ,r41 #aied1 ,,geology ,,of ,,dinosaur ,,national ,,monument ,,and ,,vicinity1 ,,utah--,,colorado4 ,utah ,geological and ,mineralogical ,survey ,bulletin #db4 ,a detailed study of the eastern ,uinta ,mountains4 ,weimer1 ,robert ,j41 and ,haun1 ,john ,d41 editors1 #aifj1 ,,guide ,,to ,,the ,,geology ,,of ,,colorado4 ,geological ,society of ,america1 ,rocky ,mountain ,association of ,geologists1 and ,colorado ,scientific ,society1 ,denver4 ,a concise summary of many aspects of ,colorado geology1 this guide includes several geological itineraries and many reference listings4 ,wolle1 ,muriel ,sibell1 #aidi1 ,,stampede ,,to ,,timberline1 ,sage ,books4 ,an excellent account of early mining activity in the state1 with many fine drawings of the early settlements4 ,,index ,a ,abrams ,mountain1 #hg ,alamosa1 #ce ,alamosa ,formation1 #fg1 #aje1 #ajf ,alma1 #gh ,ancestral ,rocky ,mountains1 #dd1 #de ,animas ,river1 #eh1 #hf ,ankareh ,formation1 #eb ,antero ,junction1 #ba ,anthracite1 #ig ,arapahoe ,conglomerate1 #fj ,arapaho ,glacier1 #gj1 #ga ,arkansas ,hills1 #ba ,arkansas ,mountain1 #gi ,arkansas ,river1 #c1 #bb1 #ce1 #ij ,arkansas ,valley1 #ba ,aspen1 ,front41 #a1 #bb1 #ce1 #ej1 #gd1 #gg1 #gh1 #hh-hi ,aspen ,mountain1 #bc1 #hh ,avon1 #bb ,b ,battlement ,mesa1 #fb ,belden ,formation1 #dd1 #aji ,benton ,shale1 #eg ,berthoud ,pass1 #ab1 #ib ,big ,thompson ,canyon1 #ab1 #ga ,big ,thompson ,river1 #fi1 #ajc1 #ajd ,black ,canyon of the ,gunnison1 #cf1 #cg1 #dd1 #ga1 #aje ,black ,hawk1 #ad1 #gg1 #gh1 #gi1 #hj ,blue ,river1 #ajc ,book ,cliffs1 #bi ,boulder1 #h1 #ad1 #cc1 #de1 #dg1 #dh1 #ej1 #ga1 #gd1 #ge1 #id1 #ih1 #ii1 #ajj1 #aja ,boulder ,county1 #gh1 #gi ,boulder ,creek1 #a1 #ae1 #ga1 #ajc ,boulder ,creek ,granite1 #ad1 #cc1 #ce ,boulder ,reservoir1 #ajc ,breckenridge1 #a1 #gh1 #hc-hd ,bross1 ,mt41 #ba ,buena ,vista1 #bb ,buffalo ,peaks1 #ba ,building stone1 #bd1 #dh1 #ej1 #ii-aja ,c ,cache la ,poudre ,river1 #ff1 #ajc ,cambrian1 #g1 #cd1 #ci ,camp ,bird1 #gh1 #hh ,canon ,city1 #c1 #aa1 #af1 #eb1 #ec1 #ge1 #id ,canon ,city ,embayment1 #af ,carbondale1 #ig ,carboniferous1 see ,mississippian1 ,pennsylvanian ,cardiff1 #ig ,carmel ,formation1 #eb ,carter ,lake1 #ajc ,castle ,creek1 #hh ,castle ,rock1 #h1 #fa1 #aab ,castle ,rock ,conglomerate1 #fj ,cave of the ,winds1 #ajf1 #ajg ,caves1 #ca1 #ajf-ajh ,cenozoic 7see also ,tertiary1 ,quaternary71 #g1 #af1 #ah1 #bf1 #bh1 #bi1 #ei-gc1 #aji ,central ,city1 #a1 #ad1 #gd1 #gg1 #gh1 #hj ,chaffee ,formation1 #db ,cherry ,creek1 #a ,cheyenne ,mountain1 #ad1 #ae1 #aaj ,cheyenne ,sandstone1 #aje ,chinle ,formation1 #ea1 #eb1 #ic1 #aja ,clay1 #ge1 #ig-ii ,clear ,creek1 #a1 #ga1 #hj ,climax1 #ba1 #gh1 #ia-ib ,climax ,granite ,porphyry1 #ia1 #ib ,coal1 #bc1 #ge1 #if-ig ,coal ,creek1 #ad1 #ae ,coal ,creek ,quartzite1 #cc ,coaldale1 #ig ,coalmont1 #ig ,cokedale1 #ig ,collegiate ,range1 #bb ,colorado ,national ,monument1 #bi1 #ca1 #dd1 #ea1 #ajh ,colorado ,river1 #c1 #bj1 #ba1 #bh1 #bi1 #ce1 #ci1 #ajc1 #ajd1 #aje1 #ajh1 #aji ,colorado ,springs1 #ad1 #ae1 #ce1 #cg1 #dh1 #ig1 #ih1 #aji ,columbia1 ,mt41 #bb ,como1 #gh1 #ig ,construction materials1 #ig-ajb ,copper1 #gd1 #ge1 #hj1 #ha1 #hc1 #hi1 #ia ,creede1 #fe1 #gh1 #hi-ij ,crested ,butte1 #bd1 #ig ,cretaceous1 #g1 #ab1 #bj1 #bc1 #bi1 #cj1 #ec1 #ef-eh1 #id1 #ie1 #ig1 #ih1 #aja1 #aje1 #ajh1 #aaj ,cripple ,creek1 #a1 #gd1 #gg1 #gh1 #ij-ia ,cross ,mountain1 #bf1 #bi ,crystal ,river1 #bd1 #ii ,culebra ,range1 #ag ,curecanti1 #aje ,curtis ,formation1 #eb ,d ,dakota ,formation1 #ab1 #ea1 #ec1 #ef1 #id1 #ig1 #aje ,dawson ,arkose1 #fj ,dawson ,butte1 #aab ,delcarbon1 #ig ,democrat1 ,mt41 #ba ,denver1 #c1 #h1 #ad1 #cc1 #ce1 #cg1 #de1 #dg1 #dh1 #eb1 #ec1 #fj1 #gd1 #hc1 #id1 #if1 #ii1 #ajj1 #ajd1 #aab1 #aac ,denver ,basin1 #h1 #ge1 #id1 #ie ,denver ,formation1 #fj1 #fb ,devonian1 #g1 #db-dc1 #hc ,dillon1 #ajd ,dinosaur ,national ,monument1 #bg1 #ec1 #ee ,durango1 #be1 #bh1 #ce1 #dg1 #eh1 #gh1 #he1 #ajb ,dyer ,dolomite1 #db ,e ,eagle1 #dg1 #aja1 #ajf ,eagle ,river1 #bb1 #dg ,edwards1 #bb ,elbert1 ,mt41 #bb ,eldorado ,springs1 #aji ,elk ,mountains1 #bd1 #fi ,empire1 #a1 #gh1 #ha ,englewood1 #aac ,entrada ,sandstone1 #ea1 #ic ,environmental geology1 #aaa-aac ,eocene1 #fd ,estes ,lake1 #ajc ,estes ,park1 #fi1 #ajd ,evans1 ,mt41 #c1 #ab ,f ,fairplay1 #gh1 #hd-he ,fairy ,cave1 #ajg ,flattop ,mountain1 #ai ,floods1 #aab-aac ,florence1 #gd1 #id ,florissant ,fossil ,beds ,national ,monument1 #fe ,fort ,carson1 #ae ,fort ,collins1 #ce1 #aja1 #ajb ,fountain ,formation1 #ab1 #ad1 #de1 #dg1 #dh ,fox ,hills ,sandstone1 #eh ,fremont ,limestone1 #dj1 #da ,frisco1 #ba ,front ,range1 #aa-af1 #cc1 #ce1 #dd1 #ej1 #ea1 #eb1 #ef1 #fj1 #fa1 #fh1 #fi1 #gj1 #ga1 #ic1 #ii1 #aja1 #ajc1 #ajg1 #aji ,frying ,pan ,river1 #aje ,fulford1 #ajg ,fulford ,cave1 #ajf ,g ,garden of the ,gods1 #d1 #ad1 #ae1 #dg1 #dh ,garfield1 ,mt41 #cj ,gas1 natural1 #a1 #bh1 #ge1 #id-if ,gems1 #ge1 #ajb ,gem ,village1 #ajb ,georgetown1 #gh1 #ha ,gilman1 #ba ,gilpin ,county1 #gh ,glen ,eyrie ,formation1 #dd ,glenwood ,canyon1 #cg1 #ci ,glenwood ,springs1 #bd1 #bi1 #ce1 #ii1 #ajg1 #aji ,gold1 #a1 #bb1 #bi1 #gd1 #ge1 #gg-ia ,golden1 #h1 #ad1 #fb1 #gd1 #gh1 #hc1 #ic1 #ih1 #aaa ,gold ,hill1 #a1 #gd1 #gh1 #gi ,gore ,creek1 #dg ,gore ,pass1 #ai1 #bj ,gore ,range1 #bj-ba1 #ce1 #fi ,gore ,range-,eagle's ,nest ,wilderness ,area1 #bj1 #ba ,granby1 #bj1 #fb ,granby ,lake1 #ajc ,grand ,hogback1 #bh1 #bi ,grand ,junction1 #bi1 #cj1 #ce1 #ee ,grand ,lake1 #ab1 #fi1 #ajc1 #ajd ,grand ,mesa1 #ce1 #fb ,grand ,valley1 #be ,gravel1 #ge1 #ig-ii ,great ,sand ,dunes ,national ,monument1 #ag1 #ah1 #gc ,green ,river1 #bg1 #ajc ,green ,river ,basin1 #d ,green ,river ,canyon1 #ca ,green ,river ,formation1 #fd1 #ie-if ,greenhorn ,formation1 #aja ,greenhorn ,peak1 #af ,groundwater1 #gf1 #aje-ajf ,gunnison1 #ce ,gunnison1 ,black ,canyon of the1 #cf1 #cg1 #dd1 #ga1 #aje ,gunnison ,river1 #ce1 #cf1 #cg1 #aje ,gypsum 7mineral71 #bb1 #cj1 #ge1 #aja-ajb ,gypsum 7town71 #dg1 #aja ,gypsum ,valley1 #cj1 #dg1 #aja ,h ,hahn's ,peak1 #ai ,harding ,sandstone1 #dj1 #da ,harvard1 ,mt41 #bb ,hayden1 #if1 #ig ,hayden ,pass1 #ag ,hermosa ,formation1 #de1 #dg ,hidden ,valley1 #fi ,horseshoe ,amphitheater1 #he ,horseshoe ,park1 #fi ,horsetooth ,reservoir1 #ajc ,huerfano ,basin1 #ce1 #fa ,i ,ice ,age1 see ,pleistocene ,iceberg ,lake1 #ff ,idaho ,springs1 #ad1 #gh1 #hj ,idaho ,springs ,formation1 #cc1 #ib ,independence ,pass1 #bb ,iron1 #a1 #ag1 #gd ,ironton1 #gh1 #hh ,j ,jewel ,lake1 #fh ,juniper ,mountain1 #bf1 #bi ,juniper ,springs1 #aji ,jurassic1 #g1 #i1 #bc1 #cf1 #eb-ee1 #ic ,k ,kremmling1 #ai1 #bj1 #fj ,l ,la ,junta1 #h1 #ce ,lake ,city1 #gg1 #gh ,lake ,county1 #gg ,lamar1 #h ,landslides1 #aaa-aab ,la ,plata ,mountains1 #bf ,laramide ,orogeny1 #ei1 #fj ,laramie ,formation1 #eg1 #eh1 #ig ,larkspur1 #aab ,la ,veta ,pass1 #ag1 #ah1 #cg ,lead1 #gd1 #ge1 #hj1 #ha1 #hb1 #hc1 #he1 #hf1 #hi 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#ig ,yule ,marble1 #bd1 #ii ,z ,zinc1 #gd1 #ge1 #hj1 #hb1 #hc1 #he1 #hf1 #hi ,zirkel1 ,mt41 #ai ,transcriber's ,notes --,retained publication information from the printed edition3 this e,book is public-domain in the country of publication4 --,in the text versions only1 text in italics is delimited by underscores4 --,in the ,,ascii version only1 subscripted numbers are preceded by underscore and delimited by brackets4