COAL    AND    OIL    IN    UINTA    COUNTY,    WYO.  349 
GEOLOGIC   RELATIONS. 
The  natural  oil  springs  in  this  area  occur  in  the  region  of  profound  disturbance  along  the 
bsaroka  fault  (Pis.  XI,  XII). 
The  Brigham  Young,  White,  and  Carter  springs  occur  along  a  secondary  fault  just  east  of 
le  main  fault  line.  This  secondary  fault  cuts  the  west  end  of  the  Aspen  tunnel,  and  the  oil 
epage  reported  in  this  tunnel  is  to  be  regarded  as  essentially  of  the  same  character  as  that 
the  neighboring  oil  springs.  In  these  cases  the  oil  issues  directly  from  faulted  Creta- 
ious  rocks,  of  Benton  age,  at  a  horizon  stratigraphically  1,600  feet  above  the  top  of  the 
ack  shales,  which  yield  oil  in  the  wells  at  Spring  Valley.  As  these  lower  shales  are  about 
000  feet  thick,  it  would  require  a  hole  2,600  feet  deep  at  the  fault  line  to  prospect  them 
lly  if  the  strata  were  horizontal,  but  as  they  are  highly  inclined,  wells  drilled  at  the  fault 
le  must  go  to  much  greater  depths.  Where,  as  at  Hilliard,  the  strata  are  overturned, 
well  at  the  fault  line,  like  the  El  Rio  Verde  well,  must  drill  through  some  of  the  strata 
rice,  and  such  a  location  is  to  be  avoided  both  because  of  the  unnecessary  duplication 
quired  and  because  the  oil  yield  will  be  smaller  than  at  greater  distances  from  the  fault, 
ring  to  loss  by  leakage  along  the  fault  line. 
In  the  vicinity  of  Fossil  the  oil  comes  from  a  group  of  springs  which,  with  the  exception  of 
casional  globules  of  oil,  are  of  the  type  commonly  found  in  the  Eocene  beds.  The  strata 
ound  these  springs  and  for  many  feet  below  belong  to  the  Wasatch.  These  beds  show  a 
ntle  anticline  with  dips  of  about  5°,  and  the  springs  occur  very  near  the  axis.  To  the 
st,  between  this  anticline  and  the  outcrop  of  the  coal-bearing  Laramie  beds,  is  a  similar 
ncline.  The  geologic  relations  of  the  adjoining  areas  indicate  conclusively  that  the  posi- 
m  and  direction  of  this  anticline  corresponds  very  nearly  with  those  of  the  underlying 
asaroka  fault,  and  that  it  has  doubtless  been  produced  by  a  slight  movement  along  this 
Jer  axis  (PI.  XII,  B).  The  oil  floating  up  through  the  water  which  has  penetrated  to  the 
-bearing  beds  along  the  fault  has  naturally,  in  the  fairly  water-logged  beds  of  the  Wasatch, 
llected  and  found  outlet  along  this  low  anticline,  which  is  at  the  same  time  the  highest 
int  stratigraphically  and  the  lowest  point  topographically,  and  is  almost  directly  over 
e  fault  line.  The  Short  Well  penetrated  red  beds  from  1,650  feet  to  the  bottom  of  the 
11 — 2,200  feet — conclusively  showing  that  it  is  situated  west  of  the  Absaroka  fault.  The 
her  wells  in  this  field  obtained  water,  with  a  little  gas  and  oil,  in  the  Wasatch  beds.  The 
nditions  here  are  manifestly  unfavorable  for  the  accumulation  of  oil  in  commercial 
antities. 
At  Spring  Valjey  in  all  wells  except  the  one  in  sec.  10,  T.  14  N.,  R.  118  Wr.,  which  will 
discussed  later,  oil  is  found  in  sandy  layers  in  a  black  shale.  Geologically  this  black  shale 
curs  in  the  basal  portion  of  the  Benton.  Failure  to  obtain  oil  has  been  recorded  in  three 
pes  of  wells:  (1)  Those  not  deep  enough  to  reach  the  oil-bearing  strata,  such  as  the 
ibergall  and  Baker  wells  (PL  XII,  B);  (2)  those  which,  because  of  irregularities  of  the 
ndy  layers  in  the  shales,  fail  to  develop  oil,  although  it  is  found  in  adjacent  wells  (exam- 
s  of  this  type  are  the  Consolidated  Oil  Company's  wells  in  the  southwest  corner  of  sec. 
T.  15  N.,  R.  118  W.);  (3)  those  located  on  the  outcrop  of  the  shales,  particularly  those 
ar  the  eastern  edge,  where  the  beds  are  less  than  500  feet  thick — such  as  the  well  of  the 
uminating  Oil  Company  in  sec.  26  and  the  well  on  the  west  side  of  sec.  24,  T.  15  N.,  R. 
8W. 
In  general,  no  oil  is  found  along  the  outcrop  of  this  bed,  but  the  amount  increases  with 
e  dip.  This,  together  with  the  irregularity  shown  in  the  position  of  the  oil-bearing  sands 
adjoining  wells  and  the  fact  that  no  water  has  been  found  in  the  oil-bearing  beds,a  suggests 
While  water  has  been  encountered  in  several  wells  in  the  Spring  Valley  region,  in  no  case  is  it  asso- 
ted  with  the  oil-bearing  strata,  and  when  the  oil  is  pumped  out  no  water  follows.  Water  occurs  more 
less  abundantly  in  the  Tertiary  beds,  as  shown  by  the  artesian  wells  in  the  vicinity  of  Fossil  and 
fe  Bettys  well  between  Tlilliard  and  Evanston.  Where  wells  are  started  in  the  Cretaceous,  water 
feometimes  found  in  the  upper  part  of  the  well,  but  the  oil-bearing  beds  are  dry.  There  are  several 
liflicting  reports  of  water  encountered  below  the  oil-bearing  beds,  but  in  these  cases,  assuming  that 
'Uer  really  was  struck  where  reported,  there  seems  to  be  no  reason  for  believing  that  it  is  in  any  way 
Bociated  with,  the  oil. 
Bull.  285—06 23 
