﻿EKDLicH.] 
  SAN 
  LUIS 
  VALLEY 
  FORMER 
  LAKES. 
  149 
  

  

  Meager 
  as 
  they 
  are, 
  they 
  tend 
  to 
  show 
  the 
  effect 
  of 
  either 
  one 
  or 
  the 
  

   other 
  kind 
  of 
  causes 
  operating 
  throughout 
  the 
  valley. 
  Of 
  interest 
  is 
  

   the 
  very 
  gradual 
  and 
  even 
  descent 
  as 
  shown 
  in 
  that 
  region 
  where 
  the 
  

   basaltic 
  strata 
  dip 
  from 
  the 
  southwest. 
  

  

  Professor 
  Stevenson 
  * 
  says 
  : 
  " 
  The 
  general 
  characteristics 
  of 
  San 
  Luis 
  

   Valiey 
  show 
  beyond 
  a 
  doubt 
  that 
  this 
  whole 
  region, 
  as 
  far 
  south 
  as 
  the 
  

   New 
  Mexico 
  border, 
  and 
  as 
  far 
  north 
  as 
  the 
  head 
  of 
  San 
  Luis 
  Eiver, 
  

   was 
  at 
  one 
  time 
  occupied 
  by 
  a 
  great 
  fresh-water 
  lake 
  covering 
  an 
  area 
  

   of 
  several 
  thousand 
  square 
  miles 
  and 
  fed 
  by 
  streams 
  coming 
  from 
  the 
  

   mountain 
  glaciers." 
  Essentially 
  this 
  statement 
  agrees 
  with 
  my 
  own 
  

   observations, 
  but 
  it 
  is 
  a 
  rather 
  general 
  one. 
  As 
  regards 
  extent 
  I 
  cannot 
  

   perfectly 
  agree 
  with 
  Professor 
  Stevenson, 
  but 
  have 
  laid 
  down 
  the 
  boun- 
  

   daries 
  of 
  my 
  lake 
  area 
  so 
  as 
  to 
  make 
  it 
  smaller 
  than 
  it 
  would 
  appear 
  

   from 
  his 
  publication. 
  Precisely 
  upon 
  what 
  the 
  assumptions 
  justifying 
  

   the 
  supposition 
  of 
  an 
  ancient 
  lake 
  are 
  based, 
  is 
  not 
  stated, 
  save 
  that 
  

   " 
  general 
  characteristics 
  " 
  be 
  regarded 
  as 
  such. 
  So 
  far 
  as 
  I 
  am 
  able 
  

   to 
  determine, 
  the 
  physical 
  character 
  of 
  the 
  dritt 
  and 
  its 
  very 
  uniform 
  

   distribution 
  over 
  certain 
  areas, 
  each 
  area 
  containing 
  drift 
  of 
  specitic 
  

   nature, 
  furnishes 
  the 
  only 
  criterion 
  for 
  decision. 
  Professor 
  Stevenson 
  

   mentions 
  "terraces" 
  as 
  existing 
  in 
  San 
  Luis 
  Valley, 
  but 
  I 
  am 
  unable 
  to 
  

   agree 
  with 
  him 
  on 
  that 
  point. 
  It 
  is 
  true 
  that 
  slight 
  undulations 
  occur, 
  

   but 
  they 
  have 
  neither 
  the 
  character 
  of 
  terraces 
  of 
  erosion, 
  nor 
  that 
  of 
  

   terraces 
  deposited 
  by 
  receding 
  water. 
  

  

  On 
  the 
  east 
  side 
  of 
  San 
  Luis 
  Valley 
  we 
  find 
  a 
  very 
  interesting 
  group 
  

   of 
  drift, 
  that 
  has 
  already 
  been 
  mentioned 
  in 
  chapter 
  I. 
  It 
  is 
  the 
  drift 
  

   that 
  I 
  have 
  designated 
  as 
  "compact." 
  Bluffs 
  of 
  considerable 
  relative 
  

   elevation 
  are 
  composed 
  of 
  numerous 
  bowlders 
  of 
  all 
  sizes. 
  Sand 
  or 
  

   clay 
  cements 
  them, 
  either 
  loosely 
  or 
  more 
  firmly. 
  Two 
  of 
  our 
  stations 
  

   were 
  located 
  upon 
  these 
  bluffs. 
  Nearly 
  all 
  the 
  drift 
  in 
  the 
  valleys 
  im- 
  

   mediately 
  adjoining 
  owes 
  its 
  origin 
  to 
  a 
  comparatively 
  rapid 
  denudation 
  

   of 
  these 
  hills. 
  No 
  doubt 
  this 
  formation 
  could— 
  if 
  studied 
  sufficiently 
  in 
  

   detail— 
  furnish 
  a 
  clew 
  as 
  to 
  the 
  early 
  formation 
  of 
  San 
  Luis 
  Valley, 
  and, 
  

   with 
  a 
  view 
  to 
  this 
  object, 
  the 
  drift 
  in 
  question 
  will 
  be 
  more 
  fully 
  

   discussed 
  in 
  Appendix 
  A, 
  when 
  treating 
  of 
  the 
  glacial 
  phenomena 
  in 
  

   Southern 
  Colorado. 
  

  

  Along 
  the 
  streams 
  in 
  San 
  Luis 
  Valley, 
  agricultural 
  pursuits 
  are 
  en- 
  

   gaged 
  in 
  by 
  Americans 
  and 
  Mexicans, 
  the 
  latter 
  more 
  particularly 
  in 
  

   the 
  southern 
  portion. 
  Owing 
  to 
  the 
  dry 
  nature 
  of 
  the 
  soil, 
  irrigation 
  

   is 
  required, 
  and 
  thereby 
  many 
  acres 
  have 
  been 
  reclaimed. 
  Near 
  the 
  

   base 
  of 
  station 
  104 
  plateau, 
  a 
  number 
  of 
  very 
  fine 
  springs 
  are 
  found, 
  

   and 
  meadows 
  receive 
  their 
  water 
  from 
  them. 
  The 
  general 
  elevation 
  of 
  

   the 
  valley 
  is 
  such 
  that 
  most 
  of 
  the 
  cereals, 
  potatoes, 
  and 
  corn 
  will 
  yield 
  

   good 
  crops. 
  What 
  the 
  result 
  of 
  forming 
  a 
  small 
  lake 
  near 
  the 
  center 
  

   of 
  tlie 
  valley 
  might 
  be, 
  can 
  be 
  deduced 
  from 
  the 
  trials 
  and 
  experiments 
  

   made 
  elsewhere. 
  As 
  soon 
  as 
  moisture 
  enters 
  the 
  soil, 
  and 
  the 
  most 
  

   superficial 
  sand 
  is 
  cither 
  removed 
  or 
  mixed 
  with 
  the 
  underlying 
  stratum, 
  

   there 
  is 
  no 
  reason 
  why 
  not 
  rich 
  crops 
  should 
  reward 
  the 
  farmer. 
  

   Wherever 
  farming 
  is 
  carried 
  on 
  in 
  the 
  valley 
  with 
  any 
  system 
  and 
  

   industry, 
  and 
  where 
  there 
  is 
  no 
  lack 
  of 
  water, 
  the 
  results 
  are 
  satisfac- 
  

   tory. 
  The 
  supply 
  that 
  can 
  be 
  obtained 
  from 
  the 
  streams 
  there 
  is 
  ade- 
  

   quate 
  to 
  but 
  a 
  very 
  small 
  portion 
  of 
  the 
  entire 
  valley. 
  More 
  water 
  is 
  

   consumed 
  here 
  than 
  perhai)s 
  at 
  many 
  other 
  places, 
  for 
  irrigating 
  pur- 
  

   poses, 
  on 
  account 
  of 
  the 
  character 
  of 
  the 
  soil, 
  which 
  necessitates 
  great 
  

   waste. 
  

  

  * 
  Report 
  of 
  the 
  Geographical 
  and 
  Geological 
  Explorations 
  West 
  of 
  the 
  One 
  Huudredih 
  

   Meridian, 
  vol. 
  iii, 
  1875, 
  p. 
  462. 
  

  

  