,,geologic ,,setting ,,of ,,the ,,john ,,day ,,country1 ,,grant ,,county1 ,,oregon ,,united ,,states ,,department ,,of ,,the ,,interior_/ ,,geological ,,survey ,illustration3 ,the town of ,john ,day1 the ,john ,day ,river valley1 and the ,strawberry ,range1 looking south and southeast4 ,the tailings piles left by gold dredges have been levelled for building sites since the photograph was taken in #aidf4 ,one of the ,pacific ,northwest's most notable outdoor recreation areas1 the 8,john ,day ,country0 in northeastern ,oregon1 is named after a native ,virginian who was a member of the ,astor expedition to the mouth of the ,columbia ,river in #ahab4 ,there is little factual information about ,john ,day except that he was born in ,culpeper ,county1 ,va4 about #aggj4 ,it is known also that in #ahaj this tall pioneer 8with an elastic step as if he trod on springs0 joined ,john ,jacob ,astor's overland expedition under ,wilson ,price ,hunt to establish a vast fur-gathering network in the western states based on a major trading post at the mouth of the ,columbia ,river4 ,the expedition arrived in the vicinity of the ,grand ,tetons1 in what is now ,wyoming1 in ,september #ahaa1 and with the onset of winter met disaster along the ,snake ,river4 ,when they ran out of food near the present site of ,twin ,falls1 ,idaho1 ,hunt divided the expedition into four parties to seek food and a feasible route through the canyons4 ,as described in ,washington ,irving's ,astoria1 the party that included ,john ,day became widely separated from the others2 experienced terrible hardships while wintering with ,indians near ,huntington2 and was eventually reduced to just ,john ,day and ,ramsey ,crooks4 ,by mid-,april of the following year1 ,day and ,crooks reached the junction of the ,columbia and ,mah-hah ,rivers1 where a band of ,indians took everything they had1 including their clothes4 ,because of this incident1 the ,mah-hah ,river was renamed the ,john ,day4 ,returning up the ,columbia to seek help from friendly ,indians1 they were rescued by a party of trappers in canoes1 and finally reached ,astoria on the #aath of ,may #ahab4 ,although the first discovery of gold in ,oregon reportedly was made in #ahde on one of the upper branches of the ,john ,day ,river by a member of an immigrant train1 the settlement of the ,john ,day ,country really began in #ahfb1 when gold was discovered in ,canyon ,creek just above ,canyon ,city4 ,since then1 possibly #cj1jjj1jjj worth of gold has been mined1 mostly from gravels in and along ,canyon ,creek and along a #aj-mile stretch of the ,john ,day ,river4 ,lumbering and ranching are now the principal industries of the region4 ,the growth of tourism in ,oregon and ,grant ,county and the accompanying increase of interest in geology have stimulated the preparation of this leaflet4 ,the ,grant ,county ,planning ,commission and ,state ,department of ,geology and ,mineral ,industries have cooperated most cordially in the program to better inform interested visitors about the geology of the country they are seeing4 ,,geologic ,,history ,the ,john ,day ,country of today covers an area of #d1jjj-e1jjj square miles in the southwestern part of the ,blue ,mountain region of ,oregon1 and is in the borderland between two major geologic provinces4 ,one1 to the north1 is the ,columbia ,plateau which consists of flat or gently tilted flows of basalt covering about #ajj1jjj square miles4 ,the other1 to the south1 is the ,basin and ,range ,province which extends into ,mexico1 and is characterized by a wide variety of complexly folded and faulted rocks4 ,the ,strawberry-,aldrich ,mountain ,range1 rising from #g1jjj to #i1jjj feet in altitude along the south side of the ,john ,day ,river valley 7see ,figure #ac on page #ba71 is part of a #aej-mile long1 east-trending mountain chain that locally separates the two provinces4 ,many features that record events in the geologic history of northeastern ,oregon may be seen in the rocks along the paved highways within the ,john ,day ,country4 ,a road log describing some of these features is included as a part of this booklet4 ,the locations of principal points of interest1 keyed in the road log to state highway mile posts1 are shown on the map accompanying the road log4 ,the known part of the geologic history of the ,john ,day ,country began with lava flows and deposition of volcanic ash1 sandstone1 shale1 and small lenses of limestone in a late ,paleozoic sea more than #bej million years ago4 ,sometime between #bjj and #bej million years ago1 peridotite and gabbro 7dark1 magnesium-rich varieties of igneous rock7 rose from great depths and1 as molten material 7magma71 invaded the preexisting marine deposits4 ,these igneous rocks now form the core of ,canyon ,mountain and can be seen along the precipitous walls of ,canyon ,creek4 ,masses of chromium ore 7chromite7 were carried upward with the molten material4 ,after erosion had exposed the peridotite and gabbro1 the area was submerged again and1 during ,late ,triassic and ,early ,jurassic time 7about #ahj million years ago71 the ,aldrich ,mountain area was part of a seaway into which lavas flowed4 ,thousands of feet of volcanic ash from active volcanoes accumulated in the sea1 and between eruptions great thicknesses of mudstone and shale were deposited4 ,the cuts along ,u4 ,s4 ,highway #cie between ,canyon ,creek and ,bear ,valley are in these rocks4 ,during part of this volcanic activity1 ,canyon ,mountain stood as a high landmass1 but finally it too was deeply buried4 ,again the region emerged and probably was dry land during the last half of ,jurassic time 7#ace to #aej million years ago74 ,in ,early ,cretaceous time1 molten material was intruded to form the granitic rocks in the ,aldrich ,mountains and near ,dixie ,butte1 northeast of ,prairie ,city4 ,the gold veins in ,canyon ,mountain and in most of the ,blue ,mountain region probably were formed at that time by solutions from the granitic magma4 ,scattered patches of fossiliferous sandstone and conglomerate like that in ,goose ,rock 7see ,figure #e on page #aj7 show that the sea encroached on the ,blue ,mountain region briefly during ,cretaceous time after erosion had exposed the granites4 ,the shoreline was not far east of the ,john ,day area4 ,for the past #fj million years1 eastern ,oregon has been a land of volcanoes1 mountain building1 and erosion4 ,after the retreat of the ,cretaceous sea and an undefined period of erosion1 volcanic eruptions from widely scattered centers during the ,eocene ,epoch buried the region under several thousand feet of volcanic rocks which now form the ,clarno ,formation2 locally these rocks consist mostly of andesitic lava flows and coarse mud-flow breccias4 ,the ,clarno ,formation was extensively folded and faulted and deeply eroded before another series of volcanoes in and somewhat east of the ,cascade ,mountains erupted rhyolitic ash that was blown eastward and deposited as the ,john ,day ,formation during the ,oligocene ,epoch4 ,the ,john ,day ,formation appears to have been restricted to a lowland area which geologists today call the ,john ,day basin1 located between the present site of the ,cascade ,mountains and the ancestral ,blue ,mountains4 ,the ,clarno and ,john ,day beds in this basin are world famous1 having yielded thousands of bones1 leaves1 and pieces of petrified wood that were buried and preserved by the volcanic ash in a manner similar to the burial of ,pompeii by the eruption of ,mt4 ,vesuvius in #gi ,a4 ,d4 ,archaic large mammals such as the titanotheres1 and small ancestors of modern mammals such as the #d-toed forest horse ,eohippus1 which was the size of a fox terrier1 roamed subtropical forests during the ,eocene ,epoch4 ,many important links in the evolutionary chain of mammals have been found in the ,john ,day fossil beds2 for example1 the #c-toed horse ,mesohippus1 which was a forest dweller the size of a sheep1 had teeth for browsing instead of grazing4 ,the modern day landscape began to take form in ,middle ,miocene time1 when the basalt flows which cover most of the area and are exposed in the walls of ,picture ,gorge 7hence their name1 ,picture ,gorge ,basalt7 buried the landscape formed on the ,john ,day ,formation and older rocks4 ,the basalt erupted from long cracks or fissures in the ,earth's crust and formed floods of very fluid lava which flowed for distances up to one hundred miles4 ,these basalts are recognized by geologists to be of a distinct type1 commonly called plateau or flood basalt4 ,basalt1 frozen in the fissures1 forms dikes that commonly weather out above the adjoining softer rocks1 as shown in the picture of ,kimberly ,dike on page #af4 ,while the ,picture ,gorge ,basalt was flooding most of the ,john ,day basin1 several volcanoes in the vicinity of ,strawberry ,mountain erupted andesitic to rhyolitic lava and ash1 and built up cones similar to ,mt4 ,hood and the other high peaks of the ,oregon ,cascades4 ,geologists have named the remnants of these cones the ,strawberry ,volcanics4 ,because these volcanoes rose several thousand feet above the top of the ,picture ,gorge ,basalt1 ash and erosional debris from them washed out over the basalt2 these materials constitute the ,mascall ,formation4 ,although the mountains were timbered1 the lowlands probably were open and grassy4 ,bones and teeth of a pony-size three-toed horse1 ,merychippus1 have been dug from the ,mascall ,formation4 ,when the eruptions ceased in ,early ,pliocene time 7about #aj million years ago71 the entire ,blue ,mountain region probably resembled the eastern part of the ,cascade ,mountains in ,oregon today1 particularly the area between ,mt4 ,hood and ,crater ,lake4 ,the present ,strawberry-,aldrich ,mountain range and the ridges and valleys north of it were formed when the ,earth's crust buckled and broke under strong compressive forces from the north and south4 ,partly by bending or folding1 and partly by breaking along the ,john ,day and other faults1 the ,strawberry-,aldrich ,mountains were gradually raised a mile and a half to two miles above the valley to the north4 ,the floor of the main ,john ,day ,river valley was filled with gravels eroded from the rising mountains and1 as the folding and faulting and erosion slowed1 an extensive1 broad1 gently sloping surface was formed on top of the valley fill4 ,while these gravels 7called the ,rattlesnake ,formation7 were accumulating1 however1 a great volcanic eruption spread an ash flow more than #ajj feet thick over the entire length of the ,john ,day valley floor2 remnants of this flow form prominent rim-rocks between the town of ,john ,day and ,picture ,gorge4 ,bones of ,hipparion1 a horse the size of a pony which had feet and teeth like modern horses1 have been found in the gravels under the ash flow4 ,,the ,,present ,,landscape ,differences in the rates of erosion of various rocks were as important as folding and faulting in forming the topographic features in the ,john ,day ,country4 ,the chief agents of erosion are chemical weathering processes that eventually break down or decompose all rocks1 and running water which carries away the weathered or partly weathered and broken material4 ,picture ,gorge is narrow because the basalts in the walls are very resistant to weathering and break along vertical joints into large blocks that do not move easily4 ,in contrast1 the ,john ,day ,river has cut a broad1 flat-floored valley in the ,mascall ,formation at the south end of ,picture ,gorge because the ashy beds weather to fine clay which is easily washed away4 ,landslides have marked the face of the ,john ,day ,country4 ,large rock masses commonly slide where steep cliffs form in soft rocks that are capped by hard resistant rocks4 ,when the cliff face becomes too high and steep1 the soft beds give way and large blocks or masses slide downward1 usually tilting backward as they move1 as shown in the diagram of ,cathedral ,rock on page #ae4 ,cathedral ,rock and two small landslides north of the river1 about two miles east of ,john ,day1 show this classic form4 ,many landslides1 however1 are just jumbled1 hummocky masses of slumped material4 ,large-scale landsliding in the ,john ,day ,formation under the ,picture ,gorge ,basalt is colorfully displayed along the river for #h miles north of ,picture ,gorge4 ,some landslides occur suddenly1 but many move forward only as fast as the toe or lower end is eroded away1 as at ,sunken ,mountain4 ,glaciers have sculptured the principal valleys that lie above an altitude of about #e1jjj feet4 ,moving ice1 hundreds of feet thick1 plucked out semi-circular amphitheaters called cirques at the heads of the valleys4 ,the #b1jjj-;foot cliffs above ,little ,strawberry ,lake were formed this way4 ,rocks held in the ice1 like the teeth of a giant rasp1 ground off irregularities and widened the valley bottoms to a broad ,u shape as the glaciers moved down the valleys4 ,the effectiveness of ice scour can be seen by comparing glaciated ,strawberry ,creek above ,strawberry ,lake 7as shown in figure #ae on page #bb7 with unglaciated ,picture ,gorge or with ,canyon ,creek just above ,canyon ,city4 ,,road ,,log ,,of ,,the ,,john ,,day 8,,loop0 ,,note3 ,mileages at lettered stops on the map 7,fig4 #a7 refer to nearby mile posts4 ,these are not in numerical order because the route covers parts of four different numbered highways4 ,by taking the tour clockwise1 the traveler will be at higher altitudes later in the day4 ,a4 #aee4d ,holliday ,rest ,area4 ,the main ,john ,day fault1 which here is buried under river gravel1 is believed to be just south of the rest area4 ,a parallel step fault 7,fig4 #b7 cuts from left to right across the southern slope of ,mt4 ,vernon ,butte about where the juniper trees thin out4 ,flows of ,picture ,gorge ,basalt in the upper part of the butte slope down to valley level on your left4 ,rocks in the foreground and to the right are rudely bedded volcanic breccias of the ,clarno ,formation4 ,the ,clarno ,formation has been raised as much as #bej feet by movement along the fault to position it against the basalt as indicated in the diagram4 ,the fault can be seen best in afternoon light in the ravine to the right1 just south of some brick-red layers in the basalt4 ,movement on the main ,john ,day fault to the south appears to have raised the rocks at least #a1jjj feet1 so the two faults have stairstepped the rock layers4 ,the main ,john ,day fault has been traced about #hj miles4 ,illustration3 ,fig4 #b4--,view of ,mount ,vernon ,butte and diagram of faulting along its south slope4 ,illustration3 ,illustration3 ,fig4 #c4--,view of the ,john ,day fault in ,mascall ,formation at the mouth of ,fields ,creek1 and its relation to the structure of the ,john ,day ,river valley4 ,b4 #add4j ,fields ,creek ,road4 ,in the road cuts just south of the highway1 the ,john ,day fault 7,fig4 #c7 passes through the ,mascall ,formation where the slope or dip of the beds changes abruptly from gently southward to steeply northward4 ,the fault continues westward under the floor of the valley4 ,fossil leaves and snails can be found in the beds south of the fault1 and #a1jjj feet farther south vertical ,picture ,gorge ,basalt flows are exposed4 ,to the north across the valley at the ,white ,hills1 beds of the ,mascall ,formation have been dropped down against the ,picture ,gorge ,basalt along the ,belshaw fault4 ,the ,white ,hills are a well-known locality for collecting fossil leaves4 ,c4 #ach4e to #ace4j ,vertical ,ribs4 ,the prominent vertical ribs1 visible south of the river in steep slopes below the high bench 7pediment71 are flows of ,picture ,gorge ,basalt tilted vertically in the north limb of the ,aldrich ,mountain anticline4 ,the ,john ,day fault follows the base of the steep front in which the ribs are exposed4 ,d4 #acb4f ,volcanic ,ash ,flow4 ,the rimrock north of the ,john ,day ,river between here and ,dayville is a volcanic ash flow that erupted about five million years ago as red hot pumice highly charged with gas4 ,a rapidly moving incandescent cloud probably filled the ancient ,john ,day ,river valley and deposited ash to a depth of more than #ajj feet over a distance of #fj to #gj miles4 ,as shown in ,figure #d1 the ash flow blankets about #bjj feet of gravels that had been deposited in the valley4 ,the rimrock and the gravels above and below it constitute the ,rattlesnake ,formation4 ,illustration3 ,fig4 #d4--,view northwest across the ,john ,day ,river valley toward ,picture ,gorge4 ,e4 #abf4j ,picture ,gorge4 ,visible to the left of ,picture ,gorge1 from north around to west1 in order of their deposition and geologic age from oldest to youngest1 are the ,picture ,gorge ,basalt1 ,mascall ,formation1 and ,rattlesnake ,formation 7,fig4 #e74 ,the ,picture ,gorge ,basalt flows and ashy beds of the ,mascall ,formation were tilted southward together and eroded before the ,rattlesnake ,formation was laid down horizontally across them4 ,picture ,gorge and the present valley were then cut by the ,john ,day ,river after the ,rattlesnake ,formation had been tilted in its turn4 ,the five benches or terraces on the basalt just east of ,picture ,gorge mark temporary halts in downcutting of the ,john ,day ,river4 ,f4 #abb4j ,thomas ,condon ,viewpoint1 ,john ,day ,fossil ,beds ,state ,park4 ,from ,picture ,gorge to the cliffs opposite1 the ,picture ,gorge ,basalts and varicolored ash beds of the ,john ,day ,formation rise together nearly #bjjj feet4 ,the basalt that caps ,sheep ,rock is an erosional remnant4 ,the lower beds in the ,john ,day ,formation are colored red by clay eroded from thick soil on the ,clarno ,formation1 which is exposed in the farthest red hill4 ,the soil was formed by tropical weathering some #cj-ce million years ago1 before the ,john ,day ,formation was laid down4 ,faulting on a small scale is illustrated in ,sheep ,rock1 where the thick olive-drab ash flow in the middle of the ,john ,day ,formation is offset #ge-ajj feet 7,fig4 #f74 ,the fault slopes about #de eastward4 ,about two miles downstream1 large-scale movement on two faults has dropped the basalt flows in ,middle ,mountain #bjjj-bejj feet4 ,one of the faults follows along the upstream base of ,middle ,mountain 7,fig4 #f74 ,illustration3 ,fig4 #e--,north-south section along the ,john ,day ,river through ,picture ,gorge and ,middle ,mountain4 ,illustration3 ,fig4 #a4--;,geologic map of the ,john ,day ,country showing log route4 ,higher-,resolution ,map ,g4 #aah4g ,munro ,area1 ,john ,day ,fossil ,beds ,state ,park4 ,the valley of the ,john ,day ,river has been widened to nearly five miles by erosion in the ,john ,day ,formation4 ,large tilted slide blocks of the ,john ,day ,formation and basalts jumbled together show how important landsliding of soft beds under hard rocks can be in widening valleys4 ,illustration3 ,fig4 #f4--,sheep ,rock from ,thomas ,condon viewpoint4 ,here one can appreciate the regularity and extent of basalt flows of the flood or plateau type1 which form the ,columbia ,plateau4 ,individual flows have been traced #ajj miles4 ,travelers will see few other rocks between here and ,the ,dalles1 ,wenatchee1 ,pendleton1 or ,spokane as they cross parts of the ,columbia ,plateau4 ,h4 #aaf4b ,cathedral ,rock4 ,the bluff called ,cathedral ,rock is the front face of a large block of the ,john ,day ,formation that has slid from the west 7,fig4 #g74 ,inside the next horseshoe bend downstream a large mass of basalt is tilted down against ,cathedral ,rock4 ,from the highway #a4a miles farther north one can see the side of the tilted block along the river1 and the same two prominent red and olive-drab ash layers in the high bluff from which the block slid4 ,the horseshoe bend was formed as the river was pushed eastward by the nose of the landslide4 ,illustration3 ,fig4 #g4--,view of ,cathedral ,rock and diagram of landsliding4 ,illustration3 ,j4 #ajg4j ,kimberly ,dike4 ,the low bluff across the river is formed by a vertical dike of basalt which is about #fj feet wide4 ,this dike cuts through the ,john ,day ,formation and1 farther north1 the ,picture ,gorge ,basalt 7,fig4 #h 74 ,it crosses the river valley diagonally and can be traced nearly four miles4 ,the dike is formed of once-molten rock that 8froze0 in a fissure which was a channelway for lava that fed a flow on the earth's surface4 ,many similar dikes are visible along the road east of ,kimberly4 ,the basaltic magma is believed to have originated at depths of #dj miles or more within the part of the earth called the mantle4 7,at #aje4c turn east on ,state ,highway #djb along the ,north ,fork of the ,john ,day ,river7 ,illustration3 ,fig4 #h4--;,basalt dike two miles south of ,kimberly4 ,k4 #e4j ,basalt ,dike4 ,a basalt dike #ae feet wide cuts basalt flows in bluffs north of the road and forms a wall #bj feet high in places2 it is visible also across the river4 ,l4 #aa4b ,parallel ,dikes4 ,two prominent parallel dikes1 among others1 form crests of hogbacks south of the river4 ,a small tapering dike cuts pink and white beds of the ,john ,day ,formation in the river bluff4 ,this dike is the southwest end of an irregular intrusive mass of basalt in which the river has cut a steep-walled gorge4 ,m4 #ac4b ,basalt ,intrusion4 ,the road is cut through #cjj feet of basalt intruded into the ,john ,day ,formation4 ,both contacts are well exposed4 ,the basalt--when molten--baked and reddened #c to #f inches of the adjacent beds4 7,at #ac4i the highway crosses the ,north ,fork of the ,john ,day ,river and follows the ,cottonwood ,creek ,valley47 ,n4 #ah4j ,irregular ,dikes4 ,above the highway several small irregular basalt dikes cut the white beds of the ,john ,day ,formation4 ,parts of the largest dike are #aj to #ae feet high4 ,o4 #bj4a ,cottonwood ,creek ,valley4 ,the view northwestward down ,cottonwood ,creek toward ,monument 7,fig4 #i7 exemplifies the development of broad valleys by erosion in soft beds of the ,john ,day ,formation under the gently warped ,picture ,gorge ,basalt4 ,to the south1 the valley ends against massive rocks of the ,clarno ,formation which were raised as a block by movement along the ,hamilton fault4 ,the red beds are in the lower part of the ,john ,day ,formation4 ,note the contrast between the irregular massive intrusion in the valley bottom west of ,monument and the thin regular basalt flows4 ,illustration3 ,fig4 #i4--,northwest view down ,cottonwood ,creek toward ,monument4 ,on your right1 the irregular contact between the ,john ,day ,formation and ,picture ,gorge ,basalt reveals an ancient landscape buried under lava flows 7,fig4 #aj74 ,some of the flows wedge out against former hillsides and one1 marked by the dry falls1 fills an old valley4 ,for the next two miles1 to the ,sunken ,mountain viewpoint1 the road winds through landslides in the ,john ,day ,formation and ,picture ,gorge ,basalt4 ,illustration3 ,fig4 #aj4--;,ancient landscape on ,john ,day ,formation buried under ,picture ,gorge ,basalt4 ,p4 #bb4j ,sunken ,mountain4 ,a small landslide in the lower part of the ,john ,day ,formation is called ,sunken ,mountain4 ,when the valley wall was over-steepened by normal stream erosion1 the jumbled material in the lower part broke away and slid down from the steep bare slopes above4 ,absence of tilted trees indicates that the slide is not very active now4 ,the bare 8badland0 slopes are being eroded by rain wash4 ,the cliffs of the ,john ,day ,formation1 which the road climbs half a mile farther east1 are the result of rapid but normal headward erosion by the creek4 ,eventually1 because of its lower elevation and steeper gradient1 this branch of ,cottonwood ,creek will intercept and behead ,deer ,creek just east of ,hamilton4 ,a photogenic perspective view of the future stream piracy can be seen from the road on the ridge just south of ,sunken ,mountain1 about a mile and a half from the highway4 ,q4 #bf4d ,long ,creek ,mountain4 ,an uplifted block of ,picture ,gorge ,basalt #adjj-aejj feet thick forms ,long ,creek ,mountain2 ,round ,basin is eroded in the ,john ,day ,formation on which the basalt rests 7,fig4 #aa74 ,the base of the basalt can be seen in road cuts on either side of ,basin ,creek4 ,the ,hamilton fault follows the gulch to the left just below the parking area1 goes up the tree-filled gulch across ,basin ,creek1 along the low ridge at the northeast edge of ,round ,basin1 and then along the northern foot of the mountain4 ,the small slab of basalt south of the fault in ,basin ,creek has been tilted about #aj north by downward drag along the fault4 ,the ,hamilton fault system extends about #ae miles farther east4 7,in ,long ,creek turn right--south--on ,u4 ,s4 ,highway #cie74 ,illustration3 ,fig4 #aa4--,view of ,long ,creek ,mountain and ,round ,basin1 and diagram of the geologic structure4 ,illustration3 ,fig4 #ab4--,north-south section across ,fox ,valley1 showing the faulted basin structure4 ,r4 #ii4e ,fox ,valley4 ,down-warped flows of ,picture ,gorge ,basalt dip toward ,fox ,valley from all sides to form a basin 7,fig4 #ab74 ,the valley is eroded out of ashy beds and gravels of the ,mascall ,formation which fill the center of the basin to an estimated depth of #ajjj-abjj feet4 ,faults form parts of the northern and southern borders of the basin4 ,the straight1 timbered1 northward-facing steep slope less than a mile southeast of the viewpoint marks a fault4 ,s4 #ahj4c ,strawberry ,range4 ,this range and the ,aldrich ,mountains form a mountain range #ej miles long2 ,strawberry ,mountain1 altitude #ijch feet above sea level1 is its highest peak4 ,the eastern two-thirds of the ,strawberry ,range 7,fig4 #ac7 was raised as a great block by uplift on the ,john ,day fault1 which follows the northern base of the mountains4 ,the rocks in ,strawberry ,mountain and to the east are mostly lavas which poured out over the land1 whereas the ,canyon ,mountain part of the range consists of gabbro and peridotite which were intruded at great depth1 like granite4 ,the valleys in the higher parts of the range1 above about #ejjj feet1 were widened from narrow ,v's to their broad ,u profiles by glaciers during the ,pleistocene ,epoch1 or ,great ,ice ,age4 ,the alluvial fans 7,rattlesnake ,formation7 in front of the mountains were built up of bouldery gravels and finer sediments4 ,these materials were eroded from the mountains1 carried by streams down the steep narrow canyons1 and spread out on the valley floor4 ,because much more material came into the ,john ,day ,river from the ,strawberry ,mountains than from the lower mountains to the north1 the river was pushed to the north side of its wide valley4 ,faulting and erosion have completely destroyed the cones of the volcanoes from which the volcanic rocks were erupted in ,miocene and ,pliocene time4 ,illustration3 ,fig4 #ac4--,panorama of the ,strawberry ,range and the ,john ,day ,river valley from the north4 ,illustration3 ,fig4 #ad4--,section through the ,strawberry ,mountain1 along ,strawberry ,creek4 ,this image in higher resolution ,strawberry ,lake and ,vicinity4 ,at ,strawberry ,camp1 about #ab miles south of ,prairie ,city1 the broad floor and steep walls of ,strawberry ,creek valley indicate that the valley has been glaciated4 ,the precipitous cliffs and rounded valley bottom above ,strawberry ,lake are characteristic of glaciated mountains 7,fig4 #ae74 ,strawberry ,lake is dammed by landslides which probably came from the west wall of the valley after the glacier melted and left the valley wall over-steepened4 ,the hummocky surface and blocky material in the slide are well shown along the last half mile of the trail to ,strawberry ,lake4 ,strawberry ,falls mark the front of a glacial step over a massive flow of platy andesite4 ,little ,strawberry ,lake is dammed by a low glacial moraine4 ,illustration3 ,fig4 #ae4--,strawberry ,lake1 the glaciated valley of ,strawberry ,creek1 and cirque walls formed by the ,strawberry volcanic plug4 ,most of the lavas in the ,strawberry ,mountains were erupted from a central vent about #djjj feet in diameter which is exposed in the cliffs above ,little ,strawberry ,lake4 ,the pinnacles known as 8,rabbit ,ears10 above the prominent talus in figure #ae1 are of vent breccias that consist mostly of welded blocks of scoriaceous basalt1 but also contain volcanic bombs which were blown out as blobs of fluid lava4 ,huge blocks of the breccia have fallen onto a gentle bare slope west of ,little ,strawberry ,lake4 ,the massive1 vertically-jointed cliffs are formed of basalt which cooled slowly and formed a plug in the throat of the volcano after the eruptions ceased4 ,the thin irregular scoriaceous andesite flows1 which are exposed in the cliffs east of ,little ,strawberry ,lake adjoining the plug1 contrast strikingly with the massive even flows of the ,picture ,gorge ,basalt4 ,tilting of the ,strawberry ,mountain block is shown by the southward dip of all the flows in the area4 ,the flows in the cliffs west of ,strawberry ,lake1 for example1 originally must have sloped northward away from the vent where they erupted4 ,their present southward dip of about #ae therefore indicates that they have been rotated more than #ae by faulting1 partly along the northern edge of the mountain range4 7,fig4 #ad 74 ,selected ,references ,to ,detailed ,reports ,u4 ,s4 ,geological ,survey ,maps3 ,no4 #a-ddg ,geologic ,map of the ,canyon ,city quadrangle1 northeastern ,oregon1 by ,c4 ,ervin ,brown and ,t4 ,p4 ,thayer1 #aiff4 ,the map covers the entire region at a scale of one inch equals #d miles4 ,,gq-#dch ,geologic ,map of the ,aldrich ,mountain quadrangle1 ,oreg41 7with text7 by ,t4 ,p4 ,thayer and ,c4 ,ervin ,brown1 #aiff4 ,,gq-#edh ,geologic ,map of the ,mount ,vernon quadrangle1 ,oreg41 7with text7 by ,c4 ,ervin ,brown and ,t4 ,p4 ,thayer1 #aiff4 ,,mf-#ea ,preliminary ,geologic ,map of the ,john ,day quadrangle1 ,oreg41 by ,t4 ,p4 ,thayer1 #aief4 ,u4 ,s4 ,geological ,survey ,professional ,papers3 ,no4 #eej-;,c ,local thickening of basalts and silicic volcanism in the ,canyon ,city quadrangle1 ,oreg41 by ,t4 ,p4 ,thayer and ,c4 ,e4 ,brown1 pages ,c#gc-;,c#gh1 #aiff4 7,from material provided by ,thomas ,p4 ,thayer7 ,illustration3 ,as the ,nation's principal conservation agency1 the ,department of the ,interior has basic responsibilities for water1 fish1 wildlife1 mineral1 land1 park1 and recreational resources4 ,indian and ,territorial affairs are other major concerns of ,america's 8,department of ,natural ,resources40 ,the ,department works to assure the wisest choice in managing all our resources so each will make its full contribution to a better ,united ,states--now and in the future4 ,transcriber's ,notes --,silently corrected several typos4 --,provided all images resized and oriented for use on a portable e,book reader4 --,provided clickable links to higher-resolution versions of detailed images4