BOOK    CLIFFS    COAL    FIELD,    UTAH.  293 
i lower  part  of  this  section  and  some  shale  is  interbedded  with  the  sandstone  in  the  upper 
part.  The  central  500  to  700  feet  of  this  sandstone  series  make  bold  cliffs  toward  the  top 
of  the  Book  Cliffs  and  Wasatch  escarpments.  In  the  Book  Cliffs  the  sandstone  is  esti- 
mated to  be  not  less  than  1,000  feet  thick.  Toward  the  west  it  either  becomes  thinner  or 
is  in  part  concealed  by  the  overlap  of  Tertiary  strata. 
STRUCTURE. 
That  part  of  the  Book  Cliffs  coal  field  west  of  Green  River  lies  on  the  outer  rim,  to  the 
north  and  west,  of  the  broad  upward  fold  known  as  the  San  Rafael  Swell.  The  Book 
Cliffs  are  on  the  northward-pitching  end  of  this  fold  and  the  rocks  dip  about  5°.  Near 
the  junction  of  the  Book  Cliffs  and  the  eastern  escarpment  of  the  Wasatch  Plateau,  at  the 
west  side  of  Price  River  Valley,  the  strike  of  the  rocks  turns  toward  the  south.  Through- 
out the  eastern  escarpment  of  the  Wasatch  Plateau,  from  Price  River  to  the  south  end 
J  of  the  field  in  eastern  Sevier  County,  the  rocks  are  almost  flat.     The  dips  are  usually 
j  toward  the  west  and  rarely  exceed  2°. 
Folds. — Huntington  Canyon  and  Pleasant  Valley  cut  deeply  into  the  northeastern  part 
of  the  Wasatch  Plateau,  exposing  the  coals  and  revealing  a  slight  upward  flexure  of  the 
rocks.  The  strata  have  been  broadly  though  slightly  warped.  The  center  of  this  swell 
is  situated  near  the  sources  of  Huntington  Canyon  and  Pleasant  Valley,  in  western  Carbon 
and  northwestern  Emery  counties.  The  swell  is  so  low  that  the  westward  inclination  of 
the  strata  due  to  the  San  Rafael  uplift  is  succeeded  by  a  horizontal  position  or  one  slightly 
inclined  toward  the  east.  The  rocks  are  inclined  at  a  lower  grade  southward  down  Hunt- 
ington Canyon.  The  dips  of  the  rocks,  however,  are  less  than  the  grade  of  the  stream. 
The  inclination  of  the  strata  is  very  low  also  toward  the  west.  The  dip  is  very  slight 
toward  the  north  from  the  head  of  Pleasant  Valley  to  Scofield.  From  Scofield  north- 
eastward, however,  the  inclination  gradually  increases  to  about  5°  in  the  vicinity  of  Colton. 
Faults. — A  series  of  parallel  normal  faults,  trending  in  a  north-south  direction,  were 
noted  toward  the  head  of  Pleasant  Valley;  also  in  Huntington  Canyon  in  the  eastern  part 
of  T.  16  S.,  R.  7  E.  The  fault  planes  are  nearly  vertical  and  the  throws  or  displacements 
vary  from  a  few  feet  to  nearly  100  feet.  Coal  prospectors  report  that  greater  faults  occur 
on  the  west  side  of  Pleasant  Valley  above  Winterquarters,  but  the  report  was  not  verified. 
A  few  faults  of  local  extent  bearing  east  and  west  were  noted  in  the  Winterquarters  mine, 
and  associated  with  them  are  parallel  thin  igneous  dikes  that  locally  coke  the  coal. 
Another  group  of  normal  faults  bearing  north  and  south  cut  the  escarpment  of  the  Wasatch 
Plateau  west  of  Ferron  and  Emery.  In  places  the  faulting  is  in  a  single  plane,  while  in 
others  it  is  compound,  resulting  in  a  series  of  steps  or  zone  of  shearing.  The  block  or 
band  of  faulted  strata  west  of  Ferron  and  Emery  varies  from  1^  to  3  miles  in  width.  The 
largest  faults  here  are  on  the  sides  of  the  block,  and  the  country  between  them  has  been 
depressed  downward  nearly  300  feet.  The  fault  scarps  facing  the  depressed  block  at  the 
north  side  of  Ferron  Canyon  are  very  pronounced.  Conglomerate  and  shale  of  supposed 
Tertiary  age  occur  on  this  downthrown  block  at  lower  elevations  than  the  Laramie  sand- 
stone on  either  side.  Several  intermediate  faults  extending  parallel  to  those  on  the  side 
deform  the  downthrown  block.  Some  of  these  minor  fault  blocks  are  tilted  so  that  the 
beds  dip  as  high  as  20°. 
COALS. 
The  workable  coal  beds  that  have  been  mined  or  prospected  to  any  important  extent 
are  found  in  the  lower  250  feet  of  the  coal-bearing  strata  described  above.  These  coals 
are  associated  with  prominent  sandstone  beds  that  can  be  recognized  with  ease  and  assur- 
ance by  the  prospector.  They  crop  out  in  the  lower  cliffs  and  in  the  more  accessible  parts 
of  the  canyons  and  valleys. 
Quality  of  the  coal— The  workable  coals  in  the  Book  Cliffs  field,  with  a  lew  except  ions 
in  the  thinner  beds,  have  the  same  physical  characteristics,  though  the  beds  range  in 
