,geology (                              
,devils ,t[]                            
,national ,monum5t                      
,wyom+                              ,by 
,,*>les ,s4 ,,rob9son                   
,a ,,contribution ,,to ,,g5]al ,,geology
        ,illu/ration3 ,,dep>tm5t ,,( ,,!
 ,,int]ior  ,m>* #c1 #aidi      ,!      
,national ,p>k ,s]vice & ! ,devils ,t[] 
,natural ,hi/ory  ,association wi%es to 
?ank ! ,unit$ ,/ates ,geological ,survey
 =  _! k9d p]mission to h ?is ,bullet9  
repr9t$ ) m9or  *anges4                 
,,cont5ts                               
,page    ,ab/ract                       
#a    ,introduction                     
#a    ,geology                          
#c        ,devils ,t[]                  
#c        ,s$im5t>y rocks               
#f            ,spe>fi% =mation          
#f            ,gypsum ,spr+ =mation     
#g            ,sundance =mation         
#g                ,/ockade ,beav] %ale  
memb]                              #h   
,hulett s&/one memb]                    

#h                ,lak memb]            
#i                ,r$wat] %ale memb]    
#i        ,/ream t]race deposits &      
alluvium                             #aj
        ,talus & l&slide mat]ial        
#aj        ,/ructure                    
#aa    ,geologic hi/ory                 
#aa    ,orig9 ( ,devils ,t[]            
#ab    ,select$ bibliography            
#ac                                     
,,illu/rations        ,,figure          
,page    #eb4--;,index map %[+ location 
( ,devils ,t[] ,national ,monum5t       
#b    #ec4;,a4--,nor?we/ side ( ,devils 
,t[] %[+ h[ ! columns tap]            or
 conv]ge & 9 places unite ne> ! top &   
are cut            by num]\s            
cross-fractures                         
#d       ,b4--,s\?we/ corn] ( ,devils   
,t[] %[+ ! columns fl>+            out &
 m]g+ to =m ! massive base              
#d    #ed4--;,g5]aliz$ section ( !      
s$im5t>y rocks ( ! ,devils              
,t[] ,national ,monum5t                 
#f                              ,a      

,,contribution ,,to ,,g5]al ,,geology   
,,geology ,,( ,,devils ,,t[] ,,national 
,,monum5t1 ,,wyom+                      
,by ,*>les ,s4 ,rob9son                 
,,ab/ract        ,devils ,t[] is a      
/eep-sid$ mass ( igne\s rock t rises    
above    ! surr\nd+ hills & ! valley ( !
 ,belle ,f\r*e ,riv] 9    ,crook ,c\nty1
 ,wyo4 ,x is compos$ ( a cry/all9e rock1
 classifi$ z    phonolite porphyry1 t :5
 fre% is gray b :i* wea!rs to    gre5 or
 br[n4 ,v]tical jo9ts divide ! rock mass
 into polygonal    columns t ext5d f j  
above ! base to ! top ( ! ,t[]4      ,! 
hills 9 ! vic9ity & at ! base ( ! ,t[]  
are compos$ (    r$1 yell[1 gre51 or    
gray s$im5t>y rocks t consi/ (          
s&/one1 %ale1 or gypsum4 ,^! rocks1 9   
aggregate ab\t #djj feet    ?ick1       
include1 f olde/ to y\nge/1 ! upp] "p ( 
!    ,spe>fi% =mation1 ( ,triassic age1 
! ,gypsum ,spr+ =mation1 (    ,middle   
,jurassic age1 & ! ,sundance =mation1 ( 
,late ,jurassic age4    ,! ,sundance    
=mation consi/s ( ! ,/ockade ,beav] %ale

 memb]1    ! ,hulett s&/one memb]1 !    
,lak memb]1 & ! ,r$wat] %ale    memb]4  
,! =mations h be5 only slightly de=m$ by
 fault+ &    fold+4 ,)9 #b1jjj to #c1jjj
 feet ( ! ,t[]1 ! /rata = !    mo/ "p   
dip at #c-e t[>ds ! ,t[]4 ,beyond ?is   
di/ance1 !y    dip at #b-e f ! ,t[]4    
,! ,t[] is believ$ to h be5 =m$ by !    
intrusion ( magma    into ! s$im5t>y    
rocks1 & ! %ape ( ! igne\s mass =m$     
by ! cool$ magma is believ$ to h be5    
ess5tially ! same z    ! ,t[] today4    
,devils ,t[] owes its impressiv5ess to  
its    resi/ance to erosion z comp>$ ) !
 surr\nd+ s$im5t>y    rocks1 & to !     
contra/ ( ! somb] color ( ! igne\s      
column    to ! brightly color$ b&s (    
s$im5t>y rocks4                         
,,introduction      ,devils ,t[]1 a mass
 ( b>e rock t rises abruptly f !        
surr\nd+ grassl&s & p9e =e/s1 is "o ( ! 
mo/ conspicu\s  geologic features ( !   
,black ,hills region4 ,because ( its    
sc5ic  beauty & sci5tific int]e/1       
,presid5t ,!odore ,roosevelt 9 #aijf    

e/abli%$ ,devils ,t[] & a small surr\nd+
 area z ! fir/  ,national ,monum5t4     
,! ,devils ,t[] ,national ,monum5t cov]s
 an area ( ab\t #b squ>e  miles ne> !   
c5t] ( ,crook ,c\nty 9 nor!a/]n ,wyom+  
7fig4 #eb74  ,a pav$ road f ! entrance (
 ! ,national ,monum5t goes s\? #g  miles
 to jo9 ,u4 ,s4 ,highway #ad at a po9t  
#bi miles nor?we/ (  ,sundance1 ,wyo41 &
 #cc miles nor!a/ ( ,moorcr(t1 ,wyo4 ,! 
entrance  to ! ,national ,monum5t may   
also be rea*$ by a road 7pav$ 9  ,wyom+7
 t goes nor!a/w>d f ! entrance1 via     
,hulett &  ,aladd91 ,wyo41 to ,belle    
,f\r*e1 ,s4 ,dak41 a di/ance ( ab\t #ed 
miles1  :]e x jo9s ,u4 ,s4 ,highways    
#bab & #he4        ,illu/ration3 ,figure
 #eb4--;,index map %[+ location (       
,devils ,t[]      ,national ,monum5t4   
,public campgr\nds & a natural hi/ory   
museum are ma9ta9$ by !  ,national ,p>k 
,s]vice at ! base ( ! ,t[] ab\t #c miles
 by pav$  road f ! ,monum5t entrance4   
,! geology ( ! ,devils ,t[] ,national   
,monum5t 0 mapp$ dur+ !  summ] ( #aied  

by ! ,u4 ,s4 ,geological ,survey 9      
collaboration ) !  ,national ,p>k       
,s]vice4 ,! "w 0 "p ( a /udy ( ! geology
 (  ! nor!rn & we/]n p>ts ( ! ,black    
,hills region conduct$ by  ! ,survey on 
behalf ( ! ,division ( ,raw ,mat]ials ( 
! ,u4 ,s4  ,atomic ,en]gy ,commission4  
,! au?or wi%es to ackn[l$ge !  assi/ance
 ( ! ,national ,p>k ,s]vice &1 9        
p>ticul>1 ,mr4 ,raymond  ,mc,intyre1    
,sup]9t5d5t ( ,devils ,t[] ,national    
,monum5t4                               
,,geology      ,! rocks expos$ 9 !      
,devils ,t[] ,national ,monum5t may be  
divid$  on ! basis ( _! orig9 into two  
g5]al types2 igne\s &  s$im5t>y4 ,! ,t[]
 itself is compos$ ( igne\s rock2 t is1 
rock  =m$ directly by cool+ &           
cry/allization ( once molt5 mat]ials4   
,! rocks expos$ 9 ! rema9d] ( ! ,monum5t
 are s$im5t>y2 t  is1 !y 7 =m$ by !     
consolidation ( fragm5tal mat]ials      
d]iv$ f o!r rocks or accumulations (    
*emical precipitates t  7 deposit$ ei!r 
on ! floors ( prehi/oric seas or ne> !  

%ores ( su* seas4 ,^! rocks1 :i* crop   
out ar\nd ! igne\s  mass1 are lay]s (   
%ale1 s&/one1 silt/one1 mud/one1 gypsum1
 &  lime/one4 ,devils ,t[] owes its     
impressiv5ess to ! diff]+ rates  (      
erosion ( ^! rock types--! s(t s$im5t>y 
rocks erode m  easily ?an ! h>d igne\s  
rock--& to ! contra/ ( ! somb]  color ( 
! igne\s column to ! brightly color$ b&s
 ( s$im5t>y  rock t surr\nd its base4   
,,devils ,,t[]    ,devils ,t[] rises    
/eeply = ab\t #fjj feet f a broad talus 
slope  at its base4 ,! top ( ! ,t[]1 at 
an altitude ( #e1aag feet1 is  ab\t     
#a1bgj feet above ! ,belle ,f\r*e ,riv]4
 ,! ,t[] is ab\t #hjj  feet 9 diamet] at
 ! base4 ,! sides rise almo/ v]tically f
 !  base = a di/ance ( f #dj to #ajj    
feet & !n slope 9 m g5tly  to =m a n>r[ 
b5*4 ,above ?is b5*1 ! sides aga9 rise  
/eeply1  at angles ( #ge to ov] #he1 to 
)9 ab\t #ajj feet ( ! top :]e  ! angle  
becomes less /eep & ! top edge ( ! ,t[] 
is some:at  r\nd$4 ,! top ( ! ,t[] is   
almo/ flat & measures ab\t #ahj feet  f 

ea/ to we/ & ab\t #cjj feet f nor? to   
s\?4    ,"o ( ! mo/ /rik+ features ( !  
,t[] is its polygonal columns  7fig4    
#ec74 ,mo/ ( ! columns are #e sid$1 b "s
 are #d & #f sid$4  ,! l>g] columns     
measure #f to #h feet 9 diamet] at _!   
base &  tap] gradually upw>d to ab\t #d 
feet at ! top4 ,! columns are  b\nd$ by 
well-develop$ smoo? jo9ts 9 ! middle "p 
( ! ,t[]1  b z ! columns tap] upw>d1 !  
jo9ts betwe5 !m1 r ?an  be+ smoo?1 may  
be wavy & "s ( ! columns may unite4     
,num]\s  cross-fractures 9 ! upp] "p ( !
 ,t[] divide ! column into  _m small    
irregul>ly %ap$ blocks 7fig4 #ec;,a74   
,illu/ration3 ,figure #ec4--;,a4        
,nor?we/ side ( ,devils ,t[] %[+      h[
 ! columns tap] or conv]ge & 9 places   
unite ne> ! top      & are cut by num]\s
 cross-fractures4        ,illu/ration3  
,figure #ec4--;,b4 ,s\?we/ corn] (      
,devils ,t[]      %[+ ! columns fl>+ out
 & m]g+ to =m ! massive      base4    ,!
 columns 9 ! c5tral & upp] p>ts ( ! ,t[]
 are almo/  v]tical b fl>e out at ! b5* 

ab\t #ajj feet above ! base 7fig4       
#ec;,b74 ,on ! s\?we/ side ! columns are
 ne>ly horizontal4 ,:]e  ! columns fl>e 
out1 sev]al columns may jo9 to =m a     
l>g]1 less  di/9ct column t m]ges ) !   
massive base4    ,at ! base ( ! t[]1    
bel[ ! b5*1 ! rock is massive &  jo9t+1 
poorly develop$4 ,"h ! jo9ts =m l>ge    
irregul>ly  %ap$ blocks r ?an columns4  
,column> jo9ts =m z ! result (          
contraction )9 a rock mass4 ,9  igne\s  
rock ! contraction is ! result ( cool+2 
t is1 ! cold  solidifi$ rock requires   
less volume ?an ! same rock :5 molt54 ,z
  a rock cools x contracts1 & ! result+ 
t5sion is 9 a plane  p>allel to ! cool+ 
surface4 ,:5 rupture takes place1 ?ree  
fractures radiate f num]\s c5t]s 9 !    
plane p>allel to !  cool+ surface4      
,ideally1 ! fractures are at #abj to ea*
 o!r4 ,if  ! c5t]s 7 ev5ly di/ribut$1 ! 
fractures f diff]5t  c5t]s w\ld jo9 =m+ 
hexagonal 7#f sid$7 columns4 ,^!        
fractures  w g deep] & deep] into ! rock
 z cool+ progresses4 ,?is  condition    

because ( _m factors1 is seldom atta9$ 9
 nature1 s !  columns may h #d1 #e1 #f1 
or ev5 m sides4    ,! rock mak+ up      
,devils ,t[] is classifi$ z phonolite   
porphyry  7,d>ton & ,o',h>ra1 #aijg1 p4 
#f7 & is ( ,t]ti>y age4 ,! fre%         
specim5s h a light- to d>k-gray or      
gre5i%-gray v f9e-gra9$  gr\ndmass )    
conspicu\s cry/als ( :ite               
feldsp>--commonly ab\t  "o-f\r? to      
"o-half in* 9 diamet]--& small] v       
d>k-gre5  cry/als ( pyrox5e4 ,on !      
wea!r$ surfaces ! phonolite porphyry  is
 a light gray or br[ni% gray4 ,li*5s    
gr[+ on ! rock may give  x a gre51      
yell[i%-gre51 or br[n color4    ,us+ a  
microscope1 ,alb]t ,johanns5 7,d>ton &  
,o',h>ra1 #aijg1 p4 #f7  id5tifi$ !     
feldsp> cry/als z a soda-ri* or?oclase &
 !  pyrox5e cry/als z augite ) an out]  
zone ( aegirite4 ,9 addition1  ph5ocry/s
 ( apatite & magnetite1 7 id5tifi$4 ,!  
gr\ndmass1  accord+ to ,johanns51       
consi/s ( or?oclase la?s 9 subp>allel   
arrangem5t1 ne$les ( aegirite1 possibly 

"s nephelite1 small cubes  ( magnetite1 
& second>y m9]als ( calcite1 kaol91     
*lorite1  analcite1 & a anisotropic     
zeolite4        ,illu/ration3 ,figure   
#ed4--;,g5]aliz$ section ( ! s$im5t>y   
rocks ( ! ,devils ,t[] ,national        
,monum5t4        ,sy/em      ,s]ies     
,=mation & memb]2 ,?ickness1 9 feet2    
,column> section2                       
,description    ,,jurassic      ,upp]   
,jurassic        ,sundance =mation      
,r$wat] %ale memb]2 #ajj2 ,gray &       
gray-gre5 %ale4 ,?9                     
f9e-gra9$ s&/ones 9 l[] "p2 ?9          
fossilif]\s                lime/ones 9  
upp] "p          ,lak memb]2 #dj-fe2    
,yell[ s(t f9e-gra9$ calc>e\s s&/one    
,hulett s&/one memb]2 #fj-gj2 ,yell[    
massive f9e-gra9$                       
calc>e\s s&/one          ,/ockade ,beav]
 %ale memb]2 #he-ajj2 ,gray & gray-gre5 
%ales                ) ?9 calc>e\s      
s&/ones      ,,uncon=mity      ,middle  
,jurassic        ,gypsum ,spr+ =mation2 
#ae-ce2 ,:ite massive gypsum int]b$d$   

) ?9 r$ mud/one    ,,uncon=mity         
,,triassic      ,spe>fi% =mation2 #ajj2 
,r$ to m>oon silt/one & s&/one          
int]b$d$ ) "s ?9 %ale                   
,,s$im5t>y ,,rocks    ,! s$im5t>y rocks 
t surr\nd ,devils ,t[] h a total expos$ 
?ickness ( ab\t #djj feet4 ,!y are      
divid$1 f olde/ to y\nge/1  into !      
,spe>fi% =mation ( ,triassic age1 !     
,gypsum ,spr+  =mation ( ,middle        
,jurassic age1 & ! ,sundance =mation (  
,late  ,jurassic age 7fig4 #ed74        
,,spe>fi% ,,=mation    ,! ,spe>fi%      
=mation crops out 9 ! s\!rn & nor!a/]n  
p>ts  ( ! ,devils ,t[] ,national        
,monum5t along ! valley ( ! ,belle      
,f\r*e ,riv] & its tribut>ies & =ms     
conspicu\s br[ni%-r$ to  m>oon cliffs t 
bord] ! ,belle ,f\r*e valley = sev]al   
miles 9  ! ,devils ,t[] region4 ,!      
=mation is #dej to #fjj feet ?ick 9 !   
nor!rn ,black ,hills area 7,d>ton1      
#aiji1 p4 #bh72 h[ev]1 only !  upp]mo/  
#ajj feet are expos$ )9 ! ,national     
,monum5t4    ,! ,spe>fi% =mation consi/s

 ( r$ to m>oon silt/one &  s&/one       
int]b$d$ ) mud/one or %ale4 ,locally1   
gre5i%-blue  %ale p>t+s are f\nd 9 !    
silt/one & s&/one4 ,! =mation  is poorly
 cem5t$ & wea!rs v easily =m+1 = ! mo/  
"p1  g5tle slopes1 z on ! nor!a/ &      
s\?we/ sides ( ! monum5t4  ,:]e x does  
=m cliffs1 z s\? ( ! ,t[]1 ! cliffs are 
cut by  _m %>p gullies4    ,no fossils h
 be5 f\nd 9 ! ,spe>fi% =mation 9 !      
,devils  ,t[] region1 b else:]e 9       
,wyom+1 /ratigraphically equival5t      
rocks conta9 l& v]tebrates ( ,triassic  
age4                                    
,,gypsum ,,spr+ ,,=mation    ,! ,gypsum 
,spr+ =mation is expos$ 9 a ?9 b almo/  
cont9u\s  b& ar\nd ! ,t[] on ! s\?we/ to
 nor!a/ sides4 ,x also crops  out ne> ! 
top ( ! small hill at ! ea/]n b\nd>y ( !
  ,national ,monum5t1 a few hundr$ feet 
nor? ( ! ,regi/ration  ,build+4 ,?is    
=mation is compos$ mo/ly ( :ite gypsum1 
:i*  /&s out conspicu\sly betwe5 ! r$   
b$s ( ! und]ly+  ,spe>fi% =mation & b$s 
( gray-gre5 %ale at ! base ( !  ov]ly+  

,sundance =mation4    ,! ,gypsum ,spr+  
=mation ranges 9 ?ickness f ab\t #ae to 
ab\t  #ce feet4 ,x is ?icke/ on ! hill  
at ! ea/]n b\nd>y ( !  ,monum5t4 ,"h !  
=mation is made up ( a l[] unit consi/+ 
( a  b$ ( :ite massive gypsum #bj feet  
?ick ov]la9 by #ad feet (  int]b$d$ :ite
 gypsum & d>k-m>oon mud/one4 ,! =mation 
is #ae  feet ?ick along ! cliff directly
 s\? ( ,devils ,t[]4 ,at ?is  place1 !  
=mation consi/s ( #ab feet ( :ite       
massive gypsum  int]b$d$ ) #a-f in* ?ick
 b$s ( d>k-m>oon mud/one ov]la9 by  #c  
feet ( d>k-br[ni%-r$ mud/one4 ,!        
diff]5ces 9 ?ickness are  prim>ily !    
result ( erosion ( ! ,gypsum ,spr+      
=mation prior to  ! deposition ( !      
,/ockade ,beav] %ale memb] ( ! ,sundance
  =mation 7,imlay1 #aidg1 p4 #bdc74     
,,sundance ,,=mation    ,! ,sundance    
=mation consi/s ( an alt]nat+ sequ5ce ( 
gre5i%-gray %ale1 light-gray to         
yell[i%-br[n s&/one &  silt/one1 & gray 
lime/one4 ,! =mation crops out above !  
gypsum  & r$ %ale ( ! ,gypsum ,spr+     

=mation on ! bluffs & l[  roll+ hills t 
surr\nd ! ,t[]4 ,! =mation consi/s ( f\r
  memb]s t are1 9 ord] ( age f olde/ to 
y\nge/1 ! ,/ockade  ,beav] %ale memb]1 !
 ,hulett s&/one memb]1 ! ,lak memb]1 &  
! ,r$wat] %ale memb] 7fig4 #ed7 7,imlay1
 #aidg1 p4 #bbg-bgc74    ,/ockade ,beav]
 %ale memb]4--,9 g5]al1 ?is memb]1      
because x is  compos$ mo/ly ( %ale1 is  
poorly expos$4 ,! be/ exposures ( !  l[]
 "p are on ! hill at ! ea/ b\nd>y ( !   
,monum5t &  along ! /eep slope s\? ( !  
,t[]4 ,! upp] "p is fairly well  expos$ 
on ! s\? side ( ! ridge nor? ( ! ,t[]1  
ne> !  nor? b\nd>y ( ! ,monum5t4 ,!     
memb] has a ?ickness ( #he to #ajj      
feet4    ,! composition diff]s          
consid]ably 9 detail f "o exposure to   
ano!r1 b 9 g5]al x consi/s ( gray-gre5  
%ale ) int]b$d$  f9e-gra9$ calc>e\s     
s&/one4 ,at ! base ( ! memb]1 at ne>ly  
all exposures1 is a ?9 s&/one1 #a to #bd
 in*es ?ick1 conta9+  black or d>k-gray 
wat]-worn *]t pebbles t h a maximum     
dim5sion ( ab\t #b in*es4 ,above ! basal

 s&1 ! l[] half ( !  memb] is compos$   
mo/ly ( gray-gre5 %ale1 :i* locally     
conta9s  "s int]b$d$ f9e-gra9$ calc>e\s 
s&/one1 ?9 s&y & %aly  lime/one or      
dolomitic lime/one1 & r>ely ?9 b$s ( r$ 
mud/one4  ,! upp] half ( ! memb] consi/s
 ( d>k-gray to gray-gre5 %ale  )        
int]b$d$ f9e-gra9$ calc>e\s s&/one t    
range f less  ?an #a foot to #f feet 9  
?ickness4    ,! contact ( ! ,/ockade    
,beav] %ale memb] ) ! ov]ly+  ,hulett   
s&/one memb] is gradational4 ,! s&/one  
becomes m  abundant 9 ! upp] "p ( !     
,/ockade ,beav] %ale1 & ! contact       
betwe5 ^? two memb]s is plac$ at t po9t 
:]e ! s&/one  makes up m ?an #ej p]c5t (
 ! rocks4    ,hulett s&/one memb]4--,!  
,hulett s&/one memb] is resi/ant to     
wea!r+ & =ms a conspicu\s1 almo/        
v]tical1 cliff t ne>ly  encircles !     
,t[]4 ,?is memb] ranges 9 ?ickness f    
ab\t #fj to #gj  feet4    ,! ,hulett    
s&/one memb] consi/s1 9 g5]al1 ( massive
  f9e-gra9$ glauconitic calc>e\s s&/one4
 ,x is typically yell[ or  br[ni% yell[ 

b locally may be p9k or r$4 ,9 ! l[] #e 
to #aj  feet ! s&/one is 9 b$s f less   
?an #a in* to #b feet ?ick  sep>at$ by  
gray or gre5i%-gray %ale p>t+s ( f less 
?an #a  in* to #f in*es ?ick4 ,_m ( !   
s&/one b$s at ! base ( !  memb] are     
ripple m>k$4    ,! #ej to #fj feet 9 !  
middle ( ! memb] consi/s ( massive b$s  
t range 9 ?ickness f #e to #bj feet4    
,?is portion is well cem5t$  & =ms !    
conspicu\s cliff se5 ?r\gh\t ! area4 ,! 
upp] #e to  #aj feet is ?9 b$d$ 7b$s f  
less ?an #a in* to #f in*es 9  ?ickness7
 locally %aly1 & poorly cem5t$4 ,?is    
grades upw>d into  ! ov]ly+ s&/one &    
silt/one ( ! ,lak memb]4    ,lak        
memb]4--,! ,lak memb] crops out above ! 
cliff ( ,hulett  s&/one t almo/         
encircles ! ,t[]1 & x und]lies a broad  
roll+ area 9 ! nor?we/]n "p ( !         
,monum5t4 ,! memb] is  r>ely expos$     
because x is compos$ ( s(t s&/one &     
silt/one  t usually wea!r to g5tle      
slopes & become cov]$ )  vegetation4 ,! 
be/ exposure is on ! /eep hill ea/ ( !  

,t[] &  nor?we/ ( ! bridge across !     
,belle ,f\r*e riv]4    ,?is memb] is #fe
 feet ?ick a few hundr$ feet ea/ ( !    
,t[]1 b  mapp+ )9 ! ,monum5t & measur$  
sections )9 a few miles (  ! ,monum5t   
indicate t ! av]age ?ickness is ab\t #de
 feet4    ,! ,lak memb] is typically    
poorly b$d$ s(t1 v f9e-gra9$  calc>e\s  
s&/one & silt/one ) a few ?9 gray-gre5  
s&y  %ale p>t+s4 ,at ! base & ne> ! top 
( ! memb] may be a few  ?9 7less ?an #a 
in* to #f in*es ?ick7 well-cem5t$ s&/one
 b$s  t =m small ridges4 ,! s&/one &    
silt/one grade almo/  imp]ceptibly f "o 
to ! o!r4 ,! color ranges f light yell[ 
br[n & yell[ to r$4 ,9 ! ,devils ,t[]   
area1 %ades ( yell[ &  yell[i% br[n are 
mo/ common4    ,! contact ( ! ,lak ) !  
ov]ly+ ,r$wat] %ale memb] c be  obs]v$  
only 9 ! exposure ea/ ( ! ,t[]4 ,"h1 !  
upp] #c feet  ( ! ,lak is a yell[i%-br[n
 calc>e\s silty s&/one ) a few          
discont9u\s s&y %ale p>t+s 7less ?an #a 
in* ?ick71 & !  l[] #c feet ( ! ov]ly+  
,r$wat] %ale consi/s ( d>k-gray-gre5    

%ale ) int]b$d$1 ?9 silty s&/one4       
,r$wat] %ale memb]4--,?is memb]         
encircles ,devils ,t[]1 b at mo/  places
 x is cov]$ by talus f ! ,t[]4 ,ev5 :]e 
x is n  cov]$ by talus1 x is poorly     
expos$4 ,x consi/s mo/ly ( %ale t       
wea!rs into g5tle slopes1 :i* are       
usually cov]$ by vegetation4  ,! ,r$wat]
 %ale is p>tly expos$ on ,fossil ,hill1 
nor?we/ ( ,devils  ,t[]1 & on ! hill 9 !
 nor?we/ corn] ( ! ,monum5t4 ,! be/     
exposures are on ,fossil ,hill4    ,!   
top ( ! ,r$wat] %ale memb] is n expos$  
)9 ! limits (  ! ,monum5t2 consequ5tly1 
! ?ickness c\ld n be det]m9$4 ,9        
surr\nd+ areas ! ,r$wat] %ale ranges 9  
?ickness f #aej to #aij  feet4 ,x is at 
lea/ #ajj feet ?ick on ! hill 9 !       
nor?we/ corn]  ( ! ,monum5t4    ,!      
,r$wat] %ale consi/s mo/ly ( light-gray 
to d>k gray-gre5 s(t  %ale4 ,9 ! l[] #bj
 or #cj feet are b$s ( yell[ s(t s&/one1
 #c  in*es to #b feet ?ick4 ,9 ! upp]   
"p1 rang+ f #ej feet above  ! base to ! 
top1 are l5ticul> b$s ( fossilif]\s     

lime/one #a  in* to #d feet ?ick4 ,two  
su* b$s ( fossilif]\s lime/one are      
expos$ on ,fossil ,hill4    ,! ,sundance
 =mation conta9s clams1 oy/]s1          
belemnites 7squids71 &  o!r m>9e fossils
 t e/abli% its age z ,late ,jurassic    
7,imlay1  #aidg1 p4 #bdd-bfd74          
,,/ream ,,t]race ,,deposits ,,&         
,,alluvium    ,/ream deposits 7alluvium7
 are f\nd 9 ! valleys ( ! small /reams  
ar\nd ! ,t[] &1 9 p>ticul>1 9 ! valley (
 ! ,belle ,f\r*e  ,riv]1 t cuts across !
 s\!a/ corn] ( ! ,monum5t4 ,!  deposits 
consi/ ( unconsolidat$ gravel1 s&1 silt1
 & mud4    ,along ! ,belle ,f\r*e ,riv]1
 nor?we/ ( ! riv] & betwe5 x &  ! ma9   
road1 ! riv] cut a t]race 9 ! ,spe>fi%  
=mation4 ,on  ! t]race 7 deposit$ gravel
 & s&4                                  
,,talus ,,& ,,l&slide ,,mat]ial    ,!   
talus & l&slides are compos$ prim>ily ( 
! mat]ial f !  ,t[] & ! ,hulett s&/one4 
,talus f ! ,t[] =ms a broad apron t     
completely surr\nds !  ,t[]4 ,! talus   
ext5ds f high on ! %\ld]s ( ! ,t[] d[n  

to  & across ! s$im5t>y rock4 ,locally1 
l&slides ( ?is talus h  ext5d$ ?r\gh    
valleys 9 ! s$im5t>y rock d[n almo/ to !
  level ( ! surr\nd+ /reams4 ,! talus f 
! ,t[] is compos$  ( fragm5ts ( !       
columns t range f a few in*es 9 diamet] 
to  l>ge sections ( ! columns z mu* z #h
 feet 9 diamet] & #be feet  long4    ,! 
cliff ( ,hulett s&/one t surr\nds ! ,t[]
 breaks (f into  rectangul> blocks t =m 
talus slopes at ! base ( ! cliffs &     
locally l>ge l&slides d[n ! hill bel[ ! 
cliffs4 ,^! blocks (  ,hulett s&/one    
range 9 size f a few in*es to _m feet 9 
diamet]4 ,! talus mat]ial f ! ,t[] has  
at sev]al places  ov]lapp$ ! cliff (    
,hulett s&/one & become mix$ ) !        
mat]ial f ! cliff4    ,ab\t #a1djj feet 
nor? ( ! ,t[] are two pat*es ( :at is   
believ$  to be talus =m$ f s$im5t>y     
rocks t once surr\nd$ !  ,t[]4 ,! talus 
consi/s ( fragm5ts ( m$ium-gra9$        
br[ni%-:ite  s&/one &1 :at is app>5tly1 
a highly silicifi$ gray or :ite         
f9e-gra9$ qu>tzite4 ,! s&/one resembles 

t f\nd 9 ! ,lakota  7,d>ton & ,o',h>a1  
#aijg1 p4 #c7 t lies ab\t #bjj feet     
/ratigraphically above ! ,r$wat] %ale 9 
! area we/ ( !  ,monum5t4    ,! s&/one &
 qu>tzite occur 9 angul> blocks t range 
f less  ?an #a in* to sev]al feet 9     
diamet]4 ,! spaces betwe5 ! blocks  are 
fill$ ) a yell[i% or br[ni%-:ite s&4    
,! ,lakota s&/one at "o "t surr\nd$ !   
,t[] & x is believ$  t ^! blocks are    
residual blocks t h n be5 remov$ by     
erosion4                                
,,/ructure    ,! s$im5t>y rocks 9 !     
,national ,monum5t1 & 9 ! surr\nd+      
area1 are g5tly fold$ into _m small     
rolls1 bas9s & domes1 :i*  locally are  
cut by faults ( small displacem5t4 ,^!  
small folds are  sup]impos$ on a l>ge   
dome t is collaps$ 9 ! middle4          
,devils ,t[] is ne> ! middle ( !        
collaps$ dome4 ,f "o-half to  ab\t a    
mile f ! ,t[] ! s$im5t>y rocks dip g5tly
 f #b to  #e away f ! ,t[] to =m a broad
 dome4 ,)9 a radius ( ab\t  #b1jjj to   
#c1jjj feet ( ! ,t[]1 ! dips *ange1 & ! 

rocks dip1 9  g5]al1 f #c to #e t[>ds ! 
,t[] to =m a %all[ /ructural  bas94 ,9 !
 bas9 itself & on ! dome are sev]al     
small folds4 ,z  an example1 ,spr+ ,no4 
#a s\?we/ ( ! ,t[] is 9 ! c5t] ( a      
comp>atively %>p syncl9e or d[n-fold at 
! edge ( ! bas94  ,fossil ,hill nor?we/ 
( ! ,t[] is ano!r small /ructural bas94 
,! b$s along ! top & on ! nor? side (   
,fossil ,hill dip f #ab  to #eb ,s4 ,^? 
on ! s\? side ( ! hill1 nor? ( ! road1  
app>5tly dip v g5tly nor?w>d4    ,?ree  
faults 7 obs]v$ 9 ! area ( ! ,national  
,monum5t4 ,two (  ! faults are 9 !      
,hulett s&/one we/ ( ! ma9 road & we/ ( 
! ,t[]1 & ! ?ird is 9 ! nor?we/]n side (
 ! ,t[] ne>  its base 7pl4 #cj74 ,!     
faults 9 ! ,hulett s&/one are probably  
v]tical1 & ! displacem5t along !m is    
believ$ to be less ?an #aj  feet4 ,!    
fault at ! base ( ! ,t[] is a l[-angle  
fault t  tr5ds nor?we/]ly4 ,! attitude (
 ?is fault at ! po9t :]e x  disappe>s   
bel[ ! talus is3 /rike1 ,n4 #da ,w42    
dip1 #ba ,,ne4 ,! fault  zone is #d to  

#ab in*es wide & is fill$ ) a           
yell[i%-gre5 clay  & %e>$ fragm5ts (    
alt]$ phonolite porphyry4 ,! rock ( !   
,t[] bel[ ?is fault is some:at alt]$2 ! 
gr\ndmass is a light  gre5i% gray1 & !  
normally %9y cry/als ( feldsp> h a dull 
e>?y lu/]4                              
,,geologic ,,hi/ory      ,! geologic    
hi/ory ( ! ,devils ,t[] area is "p ( t (
 !  ,black ,hills region4 ,! uplift ( ! 
,black ,hills & ! subsequ5t  erosion h  
expos$ ! rocks1 f :i* ! geologic hi/ory 
( !  area may be int]pret$4    ,mo/ ( ! 
rocks )9 ! area ar\nd ! ,black ,hills   
are compos$ (  s$im5ts deposit$ by wat]4
 ,^! s$im5t>y rocks1 :i* ov]lie  mu*    
old] rocks 7,precambrian71 7 deposit$ 9 
a s]ies ( successive  lay]s dur+ "t     
int]vals f ! ,cambrian p]iod to well    
into !  ,t]ti>y p]iod4 ,deposits 9 !    
anci5t seas are repres5t$ by  lime/one1 
%ale & "s s&/one2 deposits on l[ l&s    
adjac5t to  seas1 z flood pla9s &       
deltas1 by s&/one1 silt/one1 & "s       
mud/one2 & deposits along /reams by     

conglom]ate1 s&/one &  silt/one4 ,betwe5
 ! p]iods ( deposition 7 int]vals :5 !  
l& 0 relatively high1 & 9 c]ta9 areas   
all ( ! s$im5ts (  an e>li] p]iod 7     
erod$ away4    ,! olde/ =mation expos$ 9
 ! ,national ,monum5t1 ! ,spe>fi%       
=mation1 0 deposit$ dur+ ,triassic "t   
along flat l&s bord]+  ! sea4 ,arms ( ! 
sea locally invad$ ! area to leave      
deposits (  gypsum1 :i* are f\nd ne> !  
base ( ! ,spe>fi% 9 areas outside  !    
,national ,monum5t4 ,! ,gypsum ,spr+    
=mation 0 deposit$ 9 !  sea 9 ,middle   
,jurassic "t foll[+ a p]iod ( uplift &  
erosion  t occurr$ aft] ! deposition ( !
 ,spe>fi% =mation4 ,aft] !  ,gypsum     
,spr+ =mation 0 deposit$1 ! sea         
retreat$1 & ano!r  p]iod ( erosion      
foll[$ be=e ,late ,jurassic "t :5 ! sea 
invad$ ! area aga9 & ! ,sundance =mation
 0 deposit$4 ,!  dep? & conditions =    
deposition 9 ?is sea *ang$ f "t to  "t1 
z %[n by ! alt]nat+ b$s ( %ale & s&/one 
9 !  ,sundance =mation4    ,foll[+ !    
deposition ( ! ,sundance =mation1 !re 7 

sev]al  p]iods :5 ! area 0 above sea    
level & :5 ! sea cov]$ !  area4 ,dur+ ! 
p]iods :5 x 0 above sea level1 ! high]  
l&  0 erod$1 & ! s$im5ts deposit$ at a  
l[] level4 ,:5 ! area  0 cov]$ by ! sea1
 m>9e s$im5ts1 pr9cipally %ales1 7      
deposit$4 ,ne> ! end ( ! ,cretace\s     
p]iod1 ! sea made its f9al  )drawal1 & !
 s$im5ts f late ,cretace\s "t to !      
pres5t  7 deposit$ 9 fre% wat]4    ,!   
,black ,hills uplift develop$ prim>ily  
dur+ e>ly ,t]ti>y "t1  al?\gh x may h   
/>t$ 9 v late ,cretace\s "t4 ,at ?is "t 
! pres5t g5]al /ructural features ( !   
,black ,hills area 7  develop$1 &1      
probably1 ! igne\s rocks1 su* z ,devils 
,t[]1 7  intrud$ 7,jagg>1 #aija1 p4     
#bff74 ,foll[+ ?is1 ! ,black ,hills area
  0 repeat$ly uplift$1 & erosion expos$ 
! old] s$im5t>y &  intrusive rocks4 ,ev5
 today /reams cont9ue to /rip m & m rock
  f ! c\ntry1 leav+ only local deposits1
 su* z alluvium &  t]race deposits1     
along ! valleys4                        
,,orig9 ,,( ,,devils ,,t[]      ,! orig9

 ( ,devils ,t[] has be5 a matt] (       
speculation = _m  ye>s1 & ev5 today aft]
 detail$ geologic mapp+ ( ! area1 no    
conclusive pro( ( its mode ( orig9 c be 
pres5t$4    ,sev]al !ories ( ! orig9 h  
be5 propos$4 ,"o ( ! m  popul> ( ^! is t
 x is ! neck ( an ext9ct volcano        
7,c>p5t]1 #ahhh2 ,dutton & ,s*w>tz1     
#aicf74 ,ano!r !ory is t  ,devils ,t[] &
 ,miss\ri ,buttes 7a mass ( ! same type 
( rock ab\t  #d miles nor?we/ ( ! ,t[]7 
are ! remnants ( a laccoli? 7a  tabul>  
intrusive igne\s body1 ?icke/ 9 !       
middle1 & ) a  relatively level floor71 
! v5t = :i* 0 "u ,miss\ri ,buttes       
7,jagg>1 #aija1 p4 #bfd74 ,d>ton 7#aija1
 p4 #fi7 believ$ t ! ,t[] is  ! remnant 
( a laccoli?1 small] ?an ! "o propos$ by
 ,jagg>1 !  fe$+ v5t = :i* 0 und]nea? ! 
,t[]4    ,mu* m detail$ geologic "w w h 
to be done 9 ! surr\nd+  area be=e !    
mode ( orig9 ( ,devils ,t[] may be prov$
  conclusively4 ,! evid5ce ga!r$ dur+ ! 
pres5t inve/igation1  h[ev]1 sugge/s t  
,devils ,t[] is a body ( intrusive      

igne\s rock1  :i* 0 nev] mu* l>g] 9     
diamet] ?an ! pres5t base ( !  ,t[]1 &  
:i* at dep? 7#a1jjj feet or m7 is       
connect$ to a sill or  laccoli? type    
body4 ,! bases = ?is !ory are--         
#a4 ,! expos$ portion ( ! ,t[] is !     
result ( rec5t erosion4            ,at !
 "t ( its intrusion x 0 surr\nd$ &      
probably            cov]$ by sev]al     
hundr$ feet ( s$im5t>y rock4    #b4 ,!  
m9]al composition & texture are m       
typical ( %all[            intrusive    
rocks1 :i* are =m$ at dep?1 ?an         
extrusive            rocks1 :i* are =m$ 
on ! surface4    #c4 ,no evid5ce (      
extrusive igne\s activity has be5 f\nd 9
 !            surr\nd+ area4    #d4     
,miss\ri ,buttes1 ab\t #d miles to !    
nor?we/1 & ! ,t[] h            ! same   
composition s x is assum$ t !y 7 d]iv$  
f a common magma2 possibly ! magma ( a  
l>ge intrusive            body1 su* z a 
laccoli? or sill4    #e4 ,9 a well      
drill$ ab\t #a miles s\?we/ ( ,miss\ri  
,buttes1 ne>            ! c5t] ( a      

/ructural dome1 rock simil> to ! ,t[] & 
,miss\ri ,buttes 0 enc\nt]$ at ab\t     
#a1djj feet bel[ !            base (    
,miss\ri ,buttes4 ,inasmu* z ! ?ickness 
( !            s$im5t>y rocks 9 ?is area
 is normally mu* great] ?an             
?is dep?1 ! rock 9 ! drill hole probably
 repres5ts an            intrusive body1
 r ?an ! ,precambrian igne\s rocks ^u   
:i* ! y\ng] s$im5t>y rocks 7 deposit$4  
#f4 ,! relatively small am\nt ( talus1  
slope wa%1 or t]race gravel             
d]iv$ f ! ,t[] & ,miss\ri ,buttes       
sugge/s t !y            h n be5         
ext5sively erod$1 & !re=e ! orig9al     
igne\s bodies 7 n mu* l>g] ?an at       
pres5t4    #g4 ,column> jo9t+ is common 
9 intrusive bodies =m$ at               
comp>atively %all[ dep?s4      ,! foll[+
 new mat]ial has be5 add$ to ?is booklet
 by !  ,national ,p>k ,s]vice 7,devils  
,t[] ,national ,monum5t1 #aihe7    ,!   
mo/ rec5t 9 dep?1 geologic /udy (       
,devils ,t[] 0 done by ,don  ,l4        
,halv]son 7#aihj7 & pres5t$ 9 a         

diss]tation1 to ! ,graduate  ,faculty ( 
! ,univ]sity ( ,nor? ,dakota4    ,he    
/at$ t1 8,! ,miss\ri ,buttes & ,devils  
,t[]1 h[ev]1 are  necks ( ext9ct        
volcanoes :i* h be5 expos$ by erosion4  
,?is  !ory 0 fir/ propos$ by ,c>p5t]    
7#ahhh7 & lat] exp&$ by  ,dutton &      
,s*w>tz 7#aicf74 ,! mat]ial :i* f$ ^!   
volcanoes came  f a m9imum dep? ( #ah   
km4 ,evid5ce = ?is conclusion is li/$ 9 
! foll[+ /atem5ts3        #a4 ,!        
allocla/ic breccia 9 ! vic9ity ( ,devils
 ,t[] & !            ,miss\ri ,buttes is
 def9itely igne\s 9 orig9 & probably    
repres5ts p]iods ( viol5t eruption4     
#b4 ,a v def9ite simil>ity exi/s betwe5 
^! two features &            ! volcanic 
necks 9 ! ,taylor ,m\nta9 area ( ,new   
,mexico4    #c4 ,! di/9ctive columns )  
basal fl>e are also f\nd 9 !            
volcanic necks ( ! ,taylor ,m\nta9s     
7,dutton & ,s*w>tz            #aicf71 b 
h n be5 report$ 9 column>-jo9t$         
laccoli?s4    #d4 ,! ,miss\ri ,buttes & 
,devils ,t[] 7 intrud$ directly ?r\gh   

horizontal s$im5ts )\t disrupt+ !m1 ev5 
9 !            imm$iate vic9ity ( !     
igne\s bodies4    #e4 ,rec5t rese>*     
indicates t _m ( ! laccoli?ic intrusions
            9 ! ,black ,hills region may
 h be5 less passive ?an                 
previ\sly consid]$4 ,sundance ,m\nta9   
may be a mix$            volcanic cone  
consi/+ ( weld$ a% fall1 massive qu>tz  
latite1 & a% fl[ tuffs4 ,ne>by ,sug>loaf
 ,m\nta9 is            compos$ ( lay]$  
tuffs 7,fa%b\gh #aigi74    #f4 ,collapse
 ( mat]ials into p>tly evacuat$ res]voir
 *amb]s            acc\nts = !          
depressions surr\nd+ ! ,miss\ri ,buttes 
& ,devils ,t[]4 ,! #ij m ( depression at
 ! s\!rn end            ( ! ,buttes is  
difficult to expla9 ) a laccoli?ic      
model4    #g4 ,fl[ directions d$uc$ f   
ori5t$ ?9-sections & field              
obs]vations indicate mo/ly v]tical fl[4 
,x mu/ be not$            t 9 bo? igne\s
 bodies ori5tation ( "s gra9s is        
horizontal2 ?is c\ld1 h[ev]1 simply     
indicate turbul5t            fl[4    #h4

 ,! /ability field = ! analcime-liquid  
sy/em is #e kb>            m9imum 7,r\x 
& ,hamilton #aigf71 :i* indicates t !   
orig9al melt ( ,devils ,t[] & ,miss\ri  
,buttes rock _h to            orig9ate  
at a m9imum dep? ( #ah km4    #i4 ,x is 
unlikely t magma :i* _h asc5d$ f great  
dep?s &            _h j p5etrat$ !      
resi/ant ,hulett ,memb] ( !             
,sundance ,=mation1 z well z ! ,lakota &
 ,fall ,riv]            ,=mations1 w\ld 
be /opp$ abruptly by ! less resi/ant    
%ales above4 ,:5 ! magma rea*$ ! %ale   
b$s1 !            weight ( ! column (   
igne\s rock c\ld h exce$$ !             
/r5g? ( ! %ale1 caus+ ! magma to fl[    
horizontally4            ,no indication 
( horizontal spread1 h[ev]1 is obs]v$4  
,!            cont9u\sly cyl9drical %ape
 ( ! intrusions indicates            t !
 magma mov$ /eadily upw>d & probably    
rea*$ !            surface4    #aj4     
,c>bonatites h be5 f\nd1 & =mally       
report$1 9 ! ne>by            ,be>      
,lodge ,m\nta9s1 & also z fragm5ts 9 !  

allocla/ic            breccias ( !      
,miss\ri ,buttes4 ,_! pres5ce sugge/ a  
high            volatile cont5t = !     
magma & ! possibility (                 
explosive volcanism40                   
,illu/ration3 #a4        ,illu/ration3  
#b4        ,illu/ration3 #c4            
,,select$ ,,bibliography        ,c>p5t]1
 ,f4 ,r41 #ahhh1 ,notes on ! geology ( !
 ,black ,hills3            ,prelim9>y   
report ( ! ,s\? ,dakota ,s*ool ( ,m9es1 
,rapid            ,city1 ,s4 ,dak4      
,d>ton1 ,n4 ,h41 #aiji1 ,geology & wat] 
res\rces ( ! nor!rn            portion (
 ! ,black ,hills & adjo9+ regions 9 ,s\?
            ,dakota & ,wyom+3 ,u4 ,s4   
,geol4 ,survey ,pr(4 ,pap] #fe4         
,d>ton1 ,n4 ,h41 & ,o',h>ra1 ,c4 ,c41   
#aijg1 ,description ( ! ,devils         
,t[] quadrangle1 ,wyom+3 ,u4 ,s4 ,geol4 
,survey ,geol4 ,atlas1            folio 
#aej4    ,dutton1 ,c4 ,e41 & ,s*w>tz1   
,g4 ,m41 #aicf1 ,notes on ! ,jo9t+ ( !  
,devil's ,t[]1 ,wyom+3 ,j\r4 ,geology1  
v4 #dd1 no4 #f1 p4            #gag-gbh4 

,imlay1 ,r4 ,w41 #aidg1 ,m>9e ,jurassic 
( ! ,black ,hills area1 ,s\?            
,dakota & ,wyom+3 ,am4 ,assoc4          
,petroleum ,geologi/s ,bull41 v4        
#ca1 no4 #b1 p4 #bbg-bgc4    ,jagg>1 ,t4
 ,a41 ,jr41 #aija1 ,laccoli?s ( ! ,black
 ,hills3 ,u4 ,s4 ,geol4                 
,survey #ba/ ,ann4 ,report1 pt4 #c1 p4  
#afc-bij4    ,pirsson1 ,l4 ,v41 #ahid1  
,on "s phonolite rocks f ! ,black       
,hills3            ,am4 ,j\r4 ,sci41    
#c;d s]41 v4 #dg1 p4 #cda-cdf4          
,zuidema1 ,h4 ,p41 #aidh1 ,! t\r+ public
 discov]s ,mato ,tipi 7,devils          
,t[]1 ,wyo473 ,e>? ,sci5ce ,dige/1 v4   
#c1 no4 #a1 p4 #c-g4    ,halv]son1 ,d4  
,l41 #aihj1 ,geology & petrology ( !    
,devils ,t[]1            ,miss\ri       
,buttes & ,b>l[ ,canyon ,area1 ,crook   
,c\nty ,wyom+1            ,diss]tation4 
,transcrib]'s ,notes      --,publication
 in=mation is f ! orig9al pr9t copy--?is
 e-text is    public doma9 9 ! c\ntry ( 
publication4    --,sil5tly correct$     
palpable typos2 left non-/&>d spell+s & 

dialect un*ang$4    --,split s+le       
captions describ+ multiple images1 into 
multiple    captions4    --,9 ! text    
v]sions1 delimit$ italics text 9        
und]scores 7! ,,html    v]sion          
reproduces ! font =m ( ! pr9t$ book47