292  CONTRIBUTIONS   TO   ECONOMIC    GEOLOGY,    1907,    PART   II. 
South  of  the  Axial  Basin  anticline  and  west  of  the  Danforth  Hills 
lies  the  Coyote  Basin,  or  Crooked  Wash,  essentially  a  broad  syncline 
toward  which  the  coal-bearing  strata  dip  from  the  east,  north,  and 
west  and  around  which  the  rocks  outcrop  in  a  continuous  rim  except 
on  the  south  side.  A  subordinate  anticline  with  a  north-south  axis 
arches  the  strata  through  the  very  center  of  this  basin,  crossing 
White  River  at  the  mouth  of  Blacks  Gulch,  near  Piceance  Creek, 
but  does  not  bring  the  coal  rocks  to  the  surface.  West  of  the  Coy- 
ote Basin  syncline  the  structures  are  more  intimately  related  to 
the  folds  of  the  Uinta  Mountains,  as  these  features  are  more  or  less 
symmetrical  from  Blue  Mountain  southward  in  Colorado  and  also 
from  that  uplift  northward  in  the  Utah  part  of  the  region.  The 
summit  and  southern  flanks  of  Blue  Mountain  are  due  to  a  great 
anticlinal  flexure  whose  axis  extends  east  and  west  and  pitches  in 
either  direction.  At  its  eastern  extremity  it  bends  toward  the  south- 
east and  merges  with  the  western  flank  of  the  Coyote  Basin  syncline. 
To  the  west  this  fold  pitches  more  abruptly  and  disappears  very 
abruptly  near  the  Colorado-Utah  State  line.  It  has  been  called  the 
Midland  uplift  or  anticline,  a  name  given  to  it  in  the  early  work  of 
the  Hayden  Survey.  Northwest  of  the  termination  of  the  Midland 
anticline  a  similar  fold  with  axis  parallel  to  that  uplift  and  also 
pitching  to  the  west,  is  recognized  in  Section  Ridge.  This  fold 
extends  westward  as  far  as  Green  River  and  is  referred  to  as  the 
Section  Ridge  anticline.  North  of  Section  Ridge  a  still  more  pro- 
nounced arch  of  the  strata,  very  similar  in  character  and  direction 
to  the  others,  forms  the  high  ridge  known  as  Split  Mountain,  through 
which  Green  River  passes  in  a  canyon.  This  fold,  known  as  the  Split 
Mountain  anticline,  pitches  to  the  west  and  disappears  along  the 
lower  course  of  Brush  Creek  west  of  Vernal.  North  of  Split  Moun- 
tain a  broad  structural  depression  to  which  the  name  Island  Park 
syncline  is  given  lies  between  the  Split  Mountain  anticline  on  the 
south  and  the  main  Uinta  Range  on  the  north. 
South  of  Blue  Mountain  in  Colorado  a  low,  oval  dome  on  White 
River  is  known  as  the  Raven  Park  anticline,  and  this  has  already 
been  described  in  some  detail  as  an  oil  field. a  South  of  the  Raven 
Park  uplift  a  similar  though  broader  and  more  gentle  flexure  occu- 
pies an  extensive  area  on  Douglas  Creek.  It  has  been  convenient 
to  give  names  to  some  of  the  intervening  synclines,  and  such  names 
are  explained  in  the  text. 
Influence  on  distribution  of  coals. — All  these  folds  influence  the 
trend  of  the  outcrops  of  coal-bearing  rocks,  and  consequently  a  general 
knowledge  of  the  distribution  and  arrangement  of  the  folds  is  essen- 
tial to  an  understanding  of  the  relations  of  the  various  parts  of  the 
coal  fields. 
a  Gale,  H.  S.,  Geology  of  the  Rangely  oil  district,  Rio  Blanco  County.  Colo.:  Bull.  U.  S.  Geol.  Sur- 
vey No.  350,  1908. 
