﻿306 
  REPORT 
  UNITED 
  STATES 
  GEOLOGICAL 
  SURVEY. 
  

  

  regular 
  row, 
  diverging, 
  however, 
  as 
  the 
  distance 
  increases. 
  Foothills 
  

   and 
  plains 
  to 
  the 
  east 
  are 
  far 
  below 
  us, 
  and 
  the 
  latter 
  are 
  finally 
  lost, 
  

   merging 
  into 
  the 
  sky. 
  Descending 
  westward, 
  we 
  are 
  in 
  the 
  San 
  Luis 
  

   Valley, 
  with 
  its 
  sand 
  and 
  its 
  sage-brush. 
  Where 
  water 
  is 
  plenty 
  there 
  

   the 
  valley 
  is 
  agreeable. 
  It 
  is 
  our 
  plan 
  to 
  survey 
  this 
  when 
  the 
  weather 
  

   is 
  cooler,' 
  and 
  we 
  push 
  on 
  to 
  the 
  Sawatch 
  Eange. 
  A 
  high 
  volcanic 
  pla- 
  

   teau 
  we 
  find, 
  with 
  isolated 
  points 
  that 
  command 
  the 
  country. 
  Miles 
  

   upon 
  miles 
  are 
  above 
  timber-line, 
  while 
  the 
  remainder 
  is 
  covered 
  

   with 
  a 
  dense 
  growth 
  of 
  fir 
  and 
  spruce. 
  Snow 
  greets 
  us 
  everj^- 
  

   where 
  in 
  dark 
  and 
  hidden 
  corners, 
  to 
  which 
  the 
  sunlight 
  in 
  vain 
  at- 
  

   tempts 
  to 
  j)enetrate. 
  Crossing 
  from 
  the 
  waters 
  of 
  the 
  Atlantic 
  to 
  

   those 
  of 
  the 
  Pacific 
  Ocean, 
  by 
  way 
  of 
  Weeminuche 
  Pass, 
  we 
  see 
  the 
  

   west 
  side 
  of 
  our 
  plateau. 
  Viewed 
  from 
  there, 
  the 
  steep 
  slopes, 
  cut 
  

   by 
  many 
  a 
  deep, 
  precipitous 
  caiion, 
  present 
  a 
  picture 
  of 
  peaks 
  innumer- 
  

   able, 
  not 
  much 
  higher, 
  often, 
  than 
  the 
  main 
  plateau. 
  Yet, 
  as 
  we 
  are 
  

   several 
  thousand 
  feet 
  below 
  the 
  plateau's 
  level 
  we 
  look 
  up 
  to 
  them, 
  and 
  

   hence 
  their 
  appearance 
  as 
  mountains. 
  Along 
  the 
  northern 
  drainage 
  of 
  

   the 
  Eio 
  San 
  Juan 
  there 
  exists 
  a 
  beautiful 
  country. 
  Good 
  land, 
  abun- 
  

   dance 
  of 
  wood, 
  and 
  an 
  excellent 
  supply 
  of 
  water 
  we 
  find 
  in 
  these 
  upper 
  

   valleys. 
  We 
  cross 
  in 
  succession 
  one 
  stream 
  of 
  this 
  region 
  aiter 
  the 
  

   other, 
  still 
  traveling 
  on 
  westward, 
  until 
  we 
  have 
  reached 
  the 
  Animaa. 
  

   From 
  there 
  we 
  travel 
  south 
  and 
  arrive 
  at 
  the 
  Eio 
  San 
  Juan. 
  Though 
  

   much 
  water 
  starts 
  to 
  flow 
  into 
  this 
  river, 
  a 
  large 
  portion 
  of 
  it 
  never 
  

   reaches 
  the 
  stream. 
  The 
  sandstone 
  bluffs, 
  with 
  their 
  steep, 
  sandy 
  

   caiions, 
  swallow 
  much 
  of 
  the 
  moisture 
  that 
  passes 
  through 
  them, 
  and 
  

   small 
  streams 
  cannot 
  exist. 
  Beautiful 
  as 
  the 
  country 
  is 
  near 
  the 
  head- 
  

   waters 
  of 
  the 
  San 
  Juan 
  drainage, 
  just 
  so 
  desolate 
  is 
  it 
  in 
  the 
  immediate 
  

   vicinity 
  of 
  that 
  river 
  itself. 
  Dry, 
  hot, 
  and 
  sandy 
  is 
  the 
  region 
  through 
  

   which 
  we 
  travel 
  eastward. 
  After 
  we 
  had 
  completed 
  the 
  work 
  in 
  the 
  

   lower 
  country 
  we 
  once 
  more 
  ascended 
  the 
  plateau 
  and 
  found 
  the 
  con- 
  

   tinuation 
  of 
  the 
  volcanic 
  area. 
  Thence 
  we 
  passed 
  through 
  San 
  Luis 
  

   Valley, 
  and 
  crossing 
  the 
  Sangre 
  de 
  Cristo 
  Eange 
  descended 
  the 
  foot- 
  

   hills, 
  where 
  our 
  work 
  for 
  the 
  season 
  ended. 
  

  

  As 
  the 
  character 
  of 
  the 
  country 
  varied 
  so 
  did 
  the 
  geology. 
  It 
  is 
  a 
  

   well-established 
  fact 
  that 
  the 
  orographic 
  features 
  of 
  any 
  given 
  region 
  

   furnish 
  an 
  indication 
  of 
  the 
  lithological 
  nature 
  of 
  the 
  strata 
  there 
  found. 
  

   In 
  a 
  certain 
  measure, 
  therefore, 
  we 
  are 
  enabled 
  to 
  predict, 
  from 
  the 
  

   trend 
  and 
  shape 
  of 
  the 
  hills, 
  the 
  geological 
  formation 
  that 
  we 
  hope 
  or 
  

   expect 
  to 
  find. 
  Knowing, 
  for 
  instance, 
  that 
  the 
  sandstones 
  of 
  a 
  locality 
  

   are 
  of 
  Cretaceous 
  age, 
  we 
  can 
  deduce 
  from 
  the 
  peculiar 
  shape 
  of 
  bluffs 
  

   or 
  hills 
  the 
  conclusion 
  that 
  they 
  are 
  Cretaceous. 
  During 
  1875 
  these 
  

   characteristic 
  features 
  were 
  especially 
  noticeable. 
  Metamorphic 
  rocks 
  

   form 
  the 
  "backbone" 
  of 
  the 
  Sangre 
  de 
  Cristo, 
  and 
  there 
  we 
  found 
  the 
  

   highest 
  and 
  steepest 
  mountains, 
  while 
  their 
  base, 
  more 
  gently 
  sloping, 
  

   was 
  composed 
  of 
  Carboniferous 
  strata. 
  Eastward 
  from 
  the 
  range 
  the 
  

   isolated, 
  prominent 
  peaks, 
  rising 
  amid 
  a 
  sea 
  of 
  sandstone, 
  betokened 
  

   former 
  volcanic 
  activity. 
  San 
  Luis 
  Valley, 
  with 
  its 
  level 
  surface, 
  was 
  

   a 
  sure 
  indication 
  of 
  drift, 
  and 
  the 
  dome-shaped 
  mountains 
  at 
  its 
  south- 
  

   ern 
  end 
  could 
  be 
  nothing 
  but 
  volcanic. 
  The 
  extensive 
  plateau, 
  rising 
  

   at 
  places 
  into 
  lonely 
  peaks, 
  was 
  but 
  a 
  continuation 
  of 
  what 
  we 
  had 
  seen 
  

   during 
  the 
  two 
  years 
  preceding, 
  of 
  the 
  enormous 
  trachytic 
  outflow. 
  

   Beyond 
  it 
  the 
  low 
  valleys, 
  the 
  sandstone 
  blufls 
  separated 
  by 
  steep 
  

   canons, 
  and 
  the 
  gulches 
  washed 
  down 
  into 
  dark 
  shales, 
  denoted 
  Creta- 
  

   ceous. 
  Farther 
  on, 
  above 
  these, 
  the 
  original 
  mesas 
  that 
  have 
  been 
  cut 
  

   in 
  every 
  direction, 
  indicated 
  the 
  advent 
  of 
  a 
  Post-Cretaceous 
  period. 
  

  

  In 
  order 
  to 
  facilitate 
  the 
  discussion 
  of 
  the 
  district 
  surveyed 
  during 
  

  

  