COAL    AND    OIL    IN    UINTA    COUNTY,    WYO.  335 
STRUCTURE. 
The  disturbances  of  the  strata  in  this  area  are  traceable  to  two  periods — late  Cretaceous 
land  early  Tertiary. 
(1)  Near  the  close  of  the  Cretaceous  period,  between  the  Laramie  and  Evanston,  the 
main  folding  of  this  region  took  place,  producing  the  Meridian  anticline,  Lazeart  syncline, 
Absaroka  fault,  Rock  Creek  anticline,  and  associated  structural  features.  (2)  On  the 
eroded  edges  of  these  upturned  beds  the  Evanston  beds  were  laid  down,  and  some  time 
after  the  deposition  of  the  lower  Wasatch  conglomerates,  movements  along  several  of  the 
old  lines  of  deformation  tilted  and  faulted  these  younger  beds,  producing  in  some  cases 
very  high  local  dips,  often  in  directions  opposite  to  those  of  the  older  beds.  These  phe- 
nomena are  of  considerable  importance  in  indicating  the  directions  of  thrust.  The  more 
'important  of  these  disturbances  of  the  Eocene  beds  are  traceable  to  movements  along  the 
Absaroka  fault,  the  Rock  Creek-Needles  anticlinal,  and  a  secondary  fault  line  along  Bear 
River,  north  of  Evanston. 
!  The  important  structural  features  in  the  pre-Evanston  beds  in  this  area  are  from  east 
jto  west  (see  Pis.  X  and  XI):  (1)  A  rather  regular  anticline — the  Meridian  anticline;  (2)  a 
i somewhat  disturbed,  and  in  places  overturned,  syncline — the  Lazeart  syncline;  (3)  a  much 
I  broken  region  lying  between  this  syncline  and  the  fault  to  the  west;  (4)  a  large  and  very 
pers'stent  faulted  anticline,  with  a  downthrow  to  the  east — the  Absaroka  fault;  (5)  a 
somewhat  disturbed  synclinal  basin,  deeply  filled  with  Tertiary  material,  lying  between 
(the  Absaroka  fault  and  the  uplifted  and  disturbed  region  toward  the  west;  (6)  a  greatly 
i disturbed  region,  which  in  its  broader  features,  consists  of  a  somewhat  broken  anticline 
of  "  Permo-Carboniferous  "  and  Jurassic  beds,  whose  westward  flank  is  broken  by  a  number 
of  minor  irregular  folds  and  faults;  and  (7)  a  folded  and  faulted  mass  of  Upper  Carbonif- 
erous rocks — the  Crawford  Mountains. 
The  Meridian  anticline  is  almost  wholly  buried  by  Tertiary  beds,  which,  as  they  dip 
eastward  across  the  whole  anticline,  give  no  clew  to  its  position.  The  crest  of  this  anticline 
is  exposed  in  the  valley  of  Little  Muddy  Creek,  3  or  4  miles  east  of  Cumberland  and  east 
1  of  Frontier,  where  it  shows  dips  to  the  east  of  about  the  same  amount  as  those  to  the  west. 
'The  inferred  positions  of  the  coal  beds  and  oil-bearing  shale  on  its  east  side  (Pis.  X  and  XI) 
iare  based  wholly  on  the  assumption  that  this  is  a  simple  anticline.  To  the  north  it  shows 
;  some  tendency  toward  complexity,  with  one  or  more  secondary  folds  to  the  east,  and  this 
complexity  may  extend  farther  to  the  south. 
Near  Hilliard  the  Lazeart  syncline  is  entirely  overturned,  the  lower  limb  dipping  westward 
at  angles  of  from  25°  to  30°,  and  the  upper  limb  at  from  90°  to  130°.  Between  Hilliard 
and  the  Aspen  tunnel  it  returns  to  a  normal  syncline,  with  dips  of  20°  to  30°  on  the  east  and 
40°  to  75°  on  the  west.  At  Round  Mountain  it  is  again  overturned  and  perhaps  faulted, 
but  from  that  point  northward  it  appears  entirely  normal,  with  dips  on  the  west  side 
commonly  more  than  double  those  on  the  east.  The  Laramie  beds  which  occur  along  the 
deepest  parts  of  this  syncline  are  broken  by  the  rising  and  pitching  of  the  syncline  into 
three  basins — at  Hilliard,  between  Lazeart  and  Round  Mountain,  and  between  Little 
Muddy  Creek  and  a  point  2  miles  north  of  Hams  Fork. 
Between  the  Lazeart  syncline  and  the  Absaroka  fault  the  beds  are  greatly  disturbed, 
the  amount  of  disturbance  increasing  with  proximity  to  the  fault  line. 
In  the  Absaroka  fault  the  displacement  is  something  over  15,000  feet,  with  the  down- 
throw to  the  east.  In  the  Absaroka  Ridge  region  there  is  some  folding  west  of  the  fault 
line,  but  beyond  this  the  beds  dip  westward,  indicating  that  the  area  between  the  fault  and 
the  overturned  Rock  Creek  anticline  is  a  broad  syncline.  On  Sulphur  Creek  and  about 
Knight  the  Jurassic  beds  just  west  of  the  fault  suggest  a  closely  compacted  anticline, 
merging  toward  the  west  into  an  overturned  syncline  (PI.  XII,  A).  The  eastward-dipping 
Bear  River  beds  and  the  coals  near  Old  Millis  siding  (on  Sulphur  Creek,  due  south  of  Knight) 
are  clearly  on  the  upper  or  eastward  flank  of  an  overturned  syncline. 
