﻿10 
  EEPOET 
  UNITED 
  STATES 
  GEOLOGICAL 
  SURVEY. 
  

  

  rocks, 
  as 
  seen 
  in 
  the 
  caiions. 
  On 
  the 
  western 
  side 
  of 
  the 
  plateau 
  is 
  a 
  

   monoclinal 
  fold, 
  which 
  in 
  some 
  places 
  becomes 
  a 
  fault 
  of 
  300 
  to 
  500 
  feet. 
  

   One 
  of 
  the 
  most 
  curious 
  features 
  of 
  this 
  region 
  is 
  a 
  caiion 
  extending 
  

   from 
  the 
  Dolores 
  River 
  to 
  the 
  Gunnison 
  River. 
  It 
  is 
  evidently 
  the 
  bed 
  

   of 
  an 
  old 
  stream, 
  which 
  probably 
  once 
  flowed 
  toward 
  the 
  Dolores. 
  At 
  

   present, 
  there 
  are 
  in 
  it 
  two 
  creeks, 
  one 
  a 
  tributary 
  of 
  the 
  Gunnison 
  and 
  

   the 
  other 
  a 
  branch 
  of 
  the 
  Dolores, 
  the 
  latter 
  the 
  larger 
  stream 
  of 
  the 
  

   two. 
  At 
  the 
  divide 
  between 
  them, 
  the 
  caiiou 
  is 
  about 
  1,200 
  feet 
  deep, 
  

   900 
  feet 
  of 
  gneissic 
  rock 
  and 
  300 
  of 
  sedimeutaries 
  on 
  the 
  top. 
  The 
  dip 
  

   is 
  toward 
  the 
  east, 
  and 
  the 
  creek 
  flowing 
  in 
  that 
  direction 
  gradually 
  

   gets 
  higher 
  and 
  higher 
  in 
  the 
  schists, 
  and 
  finally 
  cuts 
  through 
  the 
  over- 
  

   lying 
  sandstones, 
  in 
  which 
  it 
  joins 
  the 
  Gunnison. 
  Toward 
  the 
  west, 
  

   the 
  canon 
  rapidly 
  increases 
  in 
  depth 
  until 
  it 
  is 
  3,000 
  feet 
  below 
  the 
  

   general 
  surface. 
  The 
  stream 
  on 
  this 
  side 
  cuts 
  across 
  the 
  line 
  of 
  fault- 
  

   ing 
  of 
  the 
  west 
  side 
  of 
  the 
  plateau, 
  and 
  enters 
  the 
  red 
  sandstones, 
  which 
  

   incline 
  westward. 
  In 
  these, 
  it 
  joins 
  the 
  Dolores 
  River, 
  l^oith 
  of 
  the 
  

   canon, 
  between 
  it 
  and 
  Grand 
  River, 
  the 
  Dakota 
  group, 
  which 
  prevails 
  

   to 
  the 
  southward, 
  is 
  almost 
  entirely 
  absent, 
  the 
  red 
  beds 
  forming 
  the 
  

   greater 
  part 
  of 
  the 
  surface, 
  which 
  is 
  here 
  a 
  maze 
  of 
  dry 
  caiions. 
  The 
  

   country 
  gradually 
  falls 
  off 
  toward 
  Grand 
  River, 
  the 
  western 
  line 
  of 
  

   faulting 
  becomes 
  a 
  fold, 
  and 
  the 
  eastern 
  fold, 
  which 
  is 
  also 
  faulted 
  in 
  

   places, 
  gradually 
  becomes 
  less. 
  North 
  of 
  Grand 
  River, 
  beds 
  of 
  Upper 
  

   Cretaceous 
  age 
  appear, 
  probably 
  succeeded 
  by 
  Tertiary 
  as 
  we 
  go 
  north. 
  

   On 
  the 
  San 
  Miguel 
  and 
  Dolores 
  Rivers, 
  and 
  extending 
  westward, 
  the 
  

   rocks 
  are 
  sandstones. 
  There 
  are 
  broad 
  folds 
  extending 
  across 
  the 
  coun- 
  

   try 
  whose 
  axes 
  are 
  parallel, 
  the 
  general 
  direction 
  being 
  northwest 
  and 
  

   southeast. 
  Between 
  the 
  San 
  Miguel 
  and 
  Dolores, 
  the 
  Dakota 
  group 
  

   forms 
  the 
  floor. 
  Beyond 
  the 
  Dolores, 
  the 
  red 
  beds 
  prevail, 
  capped 
  with 
  

   isolated 
  patches 
  of 
  Jurassic 
  shales, 
  and 
  underlaid 
  with 
  beds 
  of 
  Carbon- 
  

   iferous 
  age. 
  The 
  latter 
  show 
  only 
  in 
  few 
  places. 
  The 
  drainage 
  here 
  has 
  

   two 
  general 
  courses 
  at 
  right 
  angles 
  to 
  each 
  other. 
  The 
  main 
  streams 
  

   flow 
  in 
  a 
  general 
  north 
  we 
  stery 
  direction. 
  

  

  In 
  the 
  Sierra 
  la 
  Sal, 
  the 
  prevailing 
  rock 
  is 
  a 
  beautiful 
  porphyritic 
  

   trachyte, 
  which 
  in 
  some 
  places 
  has 
  included 
  masses 
  of 
  Cretaceous 
  shales. 
  

   One 
  of 
  the 
  most 
  prominent 
  peaks 
  has 
  a 
  capping 
  of 
  sandstone, 
  which 
  

   was 
  lifted 
  up 
  by 
  the 
  eruption 
  of 
  the 
  mass, 
  the 
  base 
  of 
  the 
  peak 
  being 
  

   entirely 
  of 
  trachyte. 
  There 
  are 
  evidences 
  of 
  glacial 
  action 
  here. 
  North- 
  

   west 
  and 
  west 
  of 
  the 
  group, 
  the 
  red 
  beds 
  have 
  the 
  roches 
  moutonnees 
  

   form, 
  beautifully 
  seen 
  from 
  the 
  summits 
  of 
  the 
  mountains. 
  

  

  The 
  Abajo 
  Mountains 
  are 
  of 
  porphyritic 
  trachyte, 
  similar 
  to 
  the 
  

   Sierra 
  la 
  Sal, 
  as 
  are 
  the 
  mountains 
  about 
  Lone 
  Cone, 
  wiiich 
  properly 
  

   belong 
  to 
  the 
  district 
  assigned 
  to 
  the 
  San 
  Juan 
  division. 
  

  

  The 
  work 
  of 
  the 
  fourth 
  division, 
  directed 
  by 
  G. 
  R. 
  Bechler, 
  extended 
  

   over 
  several 
  isolated 
  areas, 
  all 
  situated 
  between 
  meridians 
  104° 
  30' 
  and 
  

   106° 
  30' 
  and 
  parallels 
  38° 
  40' 
  and 
  40° 
  30', 
  or 
  from 
  the 
  foot-hills 
  of 
  the 
  

   Rocky 
  Mountains 
  to 
  the 
  Upper 
  Arkansas 
  and 
  Eagle 
  Rivers, 
  and 
  from 
  

  

  