﻿60 
  REPORT 
  UNITED 
  STATES 
  GEOLOGICAL 
  PURVEY. 
  

  

  of 
  the 
  Sierra 
  la 
  Sal 
  are 
  forined 
  by 
  erosion 
  of 
  tbe 
  surrounding 
  strata, 
  and 
  

   that 
  the 
  summits 
  of 
  these 
  mountains 
  mark 
  in 
  reality 
  the 
  level 
  of 
  former 
  

   valleys 
  down 
  which 
  the 
  volcanic 
  material 
  flowed. 
  These 
  mountains 
  will 
  

   be 
  found 
  to 
  consist 
  in 
  part 
  of 
  stratified 
  rocks 
  on 
  which 
  the 
  volcanic 
  ma- 
  

   terial 
  rests. 
  Such 
  a 
  group, 
  he 
  says,* 
  are 
  the 
  Henry 
  Mountains, 
  whose 
  

   summits 
  we 
  could 
  see 
  from 
  the 
  Sierra 
  la 
  Sal. 
  

  

  From 
  tbe 
  distant 
  view 
  obtained, 
  I 
  am 
  inclined 
  toclass 
  the 
  Henry 
  Mount- 
  

   ains 
  with 
  the 
  Sierra 
  la 
  Sal 
  and 
  Abajo, 
  as 
  their 
  outline 
  is 
  similar, 
  and 
  

   they 
  appear 
  to 
  be 
  isolated 
  as 
  the 
  former 
  are.f 
  

  

  In 
  the 
  Sierra 
  la 
  Sal, 
  on 
  the 
  highest 
  peak, 
  there 
  is 
  a 
  capping 
  of 
  sediment- 
  

   ary 
  beds. 
  In 
  others 
  there 
  are 
  included 
  fragments 
  of 
  shales 
  of 
  oSTo. 
  2 
  or 
  

   No. 
  3 
  Cretaceous, 
  highly 
  metamorphosed. 
  The 
  strata 
  surrounding 
  the 
  

   mountains 
  dip 
  from 
  the 
  central 
  mass 
  of 
  trachyte. 
  The 
  proofs 
  of 
  the 
  

   eruptive 
  character 
  of 
  the 
  mountains 
  will 
  be 
  treated 
  of 
  more 
  in 
  detail 
  

   when 
  we 
  speak 
  more 
  fully 
  of 
  the 
  trachyte 
  in 
  a 
  succeeding 
  chapter. 
  

  

  Southwest 
  of 
  the 
  Salt 
  Mountains 
  the 
  country 
  appears 
  to 
  be 
  cut 
  up 
  by 
  

   the 
  drainage 
  into 
  innumerable 
  canons. 
  The 
  rocks, 
  as 
  seen 
  from 
  the 
  

   mountains, 
  are 
  the 
  Triassic 
  red 
  sandstones 
  with 
  mesa 
  tops. 
  Through 
  

   these 
  rocks 
  the 
  Grand 
  cuts 
  its 
  canon 
  northwest 
  of 
  the 
  mountains. 
  As 
  

   we 
  approach 
  the 
  mountains 
  we 
  ascend 
  to 
  a 
  higher 
  level 
  by 
  steps. 
  Far 
  

   to 
  the 
  northwest 
  of 
  the 
  Grand 
  there 
  are 
  indications 
  of 
  folding 
  which 
  

   appears 
  to 
  be 
  comparatively 
  gentle. 
  It 
  is 
  improbable 
  that 
  the 
  axes 
  of 
  

   these 
  folds 
  radiate 
  from 
  the 
  mountains. 
  West 
  and 
  southwest 
  of 
  station 
  

   69 
  the 
  sedimentary 
  beds 
  (whether 
  Cretaceous 
  or 
  older 
  I 
  was 
  unable 
  to 
  

   determine 
  definitely) 
  dip 
  steeply 
  from 
  the 
  mountains, 
  the 
  line 
  of 
  out- 
  

   crop 
  curving 
  around 
  the 
  ridge 
  south 
  of 
  the 
  station, 
  and 
  extending 
  towai^d 
  

   the 
  north 
  between 
  stations 
  6S 
  and 
  69. 
  

  

  Ten 
  or 
  twelve 
  miles 
  south 
  of 
  station 
  69 
  is 
  an 
  anticlinal 
  valley, 
  the 
  

   western 
  side 
  of 
  which 
  has 
  a 
  wall 
  inclining 
  at 
  a 
  high 
  angle 
  dipping 
  to 
  

   the 
  southwest. 
  Beyond 
  it 
  is 
  the 
  Canon 
  Colorado, 
  so 
  named 
  from 
  the 
  

   bright-red 
  color 
  of 
  the 
  rocks. 
  There 
  are 
  a 
  number 
  of 
  gashes 
  in 
  the 
  

   wall 
  referred 
  to, 
  cut 
  at 
  right 
  angles 
  to 
  its 
  axis, 
  marking 
  the 
  course 
  of 
  

   streams 
  which, 
  in 
  rainy 
  seasons, 
  flow 
  to 
  the 
  southwest, 
  in 
  the 
  direction 
  

   of 
  the 
  dip, 
  to 
  the 
  Canon 
  Colorado. 
  The 
  caiion 
  leads 
  toward 
  the 
  north- 
  

   west 
  to 
  Grand 
  River. 
  About 
  its 
  sources 
  are 
  narrow 
  valleys, 
  bordered 
  

   by 
  bluffs 
  of 
  red 
  sandstone, 
  which 
  becomes 
  white 
  near 
  the 
  top, 
  and 
  is 
  in 
  

   places 
  surmounted 
  by 
  Jurassic 
  strata. 
  The 
  beds 
  appear 
  to 
  be 
  horizontal, 
  

   and 
  in 
  many 
  places 
  have 
  cave-liUe 
  holes 
  worn 
  by 
  rain 
  and 
  wind. 
  As 
  

   we 
  approach 
  the 
  Sierra 
  Abajo, 
  there 
  seems 
  to 
  be 
  a 
  dip 
  in 
  the 
  sediment- 
  

   aries 
  away 
  from 
  that 
  group 
  of 
  mountains. 
  

  

  The 
  Abajo 
  Mountains, 
  or, 
  as 
  they 
  are 
  often 
  called. 
  Blue 
  Mountains, 
  are 
  

   wooded 
  from 
  base 
  to 
  summit. 
  Mr. 
  Jackson, 
  photographer 
  of 
  the 
  sur- 
  

   vey, 
  traveled 
  around 
  the 
  southern 
  end 
  of 
  them, 
  and 
  is 
  of 
  the 
  opinion 
  

   that 
  they 
  are 
  trachyte.| 
  On 
  the 
  south 
  and 
  west 
  the 
  stratified 
  rocks 
  

   (red 
  beds) 
  appear 
  to 
  jut 
  against 
  the 
  mountains, 
  reaching 
  away 
  from 
  

   them 
  in 
  a 
  series 
  of 
  steps 
  or 
  terraces. 
  The 
  line 
  of 
  junction 
  cannot 
  be 
  

   seen 
  on 
  account 
  of 
  the 
  timber. 
  Some 
  distance 
  to 
  the 
  northeast 
  of 
  the 
  

   mountains 
  I 
  noticed 
  Cretaceous 
  strata. 
  The 
  divide 
  between 
  the 
  Dolores 
  

   and 
  the 
  branches 
  of 
  the 
  San 
  Juan 
  is 
  a 
  broad 
  plateau-like 
  country 
  with 
  

   a 
  gentle 
  slope 
  toward 
  the 
  southwest. 
  The 
  branches 
  of 
  the 
  San 
  Juan 
  

  

  * 
  Exploration 
  of 
  the 
  Colorado 
  River 
  of 
  the 
  West, 
  paf^e 
  178. 
  

  

  t 
  Since 
  writing 
  the 
  above, 
  I 
  see 
  that 
  the 
  Henry 
  Mountains 
  are 
  exactly 
  similar 
  to 
  the 
  Sierra 
  

   la 
  Sal. 
  (See 
  report 
  on 
  Uinta 
  Mountains, 
  p. 
  20. 
  ) 
  

  

  t 
  Since 
  writing 
  above 
  I 
  learn 
  that 
  Newberry 
  visited 
  the 
  eastern 
  border 
  of 
  the 
  range 
  and 
  

   determined 
  them 
  to 
  be 
  eruptive. 
  (See 
  Macomb's 
  report, 
  p. 
  100.) 
  In 
  Mr. 
  Holmes's 
  report 
  a 
  

   full 
  description 
  of 
  the 
  Sierra 
  Abajo 
  will 
  be 
  found. 
  

  

  