GOLD    IN    UINTA    COUNTY,  WYO.,  AND    ON    SNAKE    RIVER.  73 
STRUCTURE. 
The  main  disturbance  in  this  area  occurred  near  the  close  of  the 
Cretaceous  period,  during  the  interval  marked  by  the  unconformity 
between  the  lower  Laramie  and  Evanston  a  formations.  A  second  and 
minor  disturbance  occurred  after  the  deposition  of  the  Evanston 
beds.  The  movement  during  this  disturbance  was  for  the  most  part 
along  several  of  the  old  lines  of  weakness,  faulting  and  tilting  the 
younger  beds  so  that  they  dip  in  some  places  from  40°  to  50°  and  in  an 
opposite  direction  to  the  older  underlying  beds.  A  third  disturbance 
may  have  occurred  between  the  deposition  of  Jurassic  and  the  Bear 
River.  There  are  some  evidences  indicating  that  the  lower  Creta- 
ceous is  entirely  wanting  in  this  area,  but  this  has  not  been  positively 
proved.  There  was,  however,  at  this  time  no  great  disturbance  asso- 
ciated with  folding  and  faulting,  for  throughout  the  area  the  Bear 
River  formation  is  apparently  conformable  upon  the  known  Jurassic 
beds. 
The  principal  structural  features  of  this  region  are  parallel  to  each 
other  and  have  a  north-south  trend  with  a  slight  westward  deflection, 
which  increases  toward  the  north.  These  are  the  direct  northward 
continuation  of  the  faults  arid  folds  observed  in  the  northern  portion 
of  the  area  mapped  in  southern  Uinta  County  during  the  summer  of 
1905.  The  important  structural  features  at  the  south  end  of  the  area 
here  considered,  named  hi  order  from  east  to  west,  are  (1)  a  rather 
regular  anticline,  with  two  or  more  secondary  folds — the  Meridian 
anticline;  (2)  a  rather  regular  syncline,  in  places  slightly  overturned — 
the  Lazeart  syncline;  (3)  a  large  and  persistent  faulted  anticline,  with 
a  downthrow  to  the  east  and  a  displacement  of  14,000  to  15,000  feet; 
and  (4)  a  broad  syncline— the  Fossil  syncline — which  lies  for  the  most 
part  west  of  this  area.  To  the  north  the  structural  conditions 
become  more  complicated.  Several  new  folds  and  faults  occur,  and 
the  entire  region  is  more  disturbed,  giving  rise  to  the  Hoback,  Wyo- 
ming, and  Salt  River  ranges.  The  important  structural  features  at 
the  north  end  of  the  area,  named  in  order  from  east  to  west,  are  (1)  a 
rather  irregular,  complex  anticlinorium  which  gives  rise  to  the  Hoback 
Range  and  passes  toward  the  south  into  a  regular  anticline;  (2)  a 
synclinorium,  the  south  end  of  which  is  a  monosyncline,  with  beds 
dipping  from  25°  to  45°  W. ;  (3)  a  faulted  anticline,  with  a  downthrow 
to  the  east  and  a  displacement  of  about  15,000  feetr;  (4)  the  north- 
ward continuation  of  the  Lazeart  syncline,  which  develops  a  sec- 
ondary fold  in 'the  vicinity  of  Snake  River;   (5)  the  northward  con- 
a  Evanston  as  here  used  is  the  same  as  the  Evanston  formation  in  southwestern  Uinta  County.  (See 
contributions  to  Economic  Geology,  1905:  Bull.  U.  S.  Geol.  Survey  No.  285,  1906,  pp.  332,  335.)  C  A. 
White  (Eleventh  Ann.  Rept.  U.  S.  Geol.  and  Geog.  Survey  Terr.,  1879,  pp.  240-241)  used  the  name  "Evans- 
ton coal  series"  in  referring  to  the  coal-bearing  beds  of  Almy  below  the  Wasatch  and  above  the  Bear 
River.  Lesquereux  (Sixth  Ann.  Rept.  Geol.  Survey  Terr.,  1873,  p.  409)  used  the  term  "Evanston 
deposits." 
