﻿EXDLicH] 
  SAN 
  LUIS 
  VALLEY 
  DEAINAGE. 
  141 
  

  

  In 
  spite 
  of 
  the 
  high 
  surroundiug 
  mountaius, 
  San 
  Luis 
  Valley 
  is 
  not 
  

   well 
  watered. 
  As 
  above 
  mentioned, 
  San 
  Luis 
  Creek 
  flows 
  through 
  Ho- 
  

   man's 
  Park, 
  but 
  is 
  soon 
  lost 
  in 
  the 
  sand 
  and 
  gravel 
  of 
  the 
  succetding 
  

   I)lain, 
  except 
  duriug 
  the 
  " 
  raiuy 
  season." 
  Numerous 
  rapid 
  mountain- 
  

   streams 
  rise 
  in 
  the 
  feaugre 
  de 
  Oristo 
  Eange, 
  flow 
  but 
  a 
  short 
  distance 
  

   beyond 
  the 
  base 
  of 
  the 
  mountains, 
  and 
  then 
  share 
  a 
  like 
  fate. 
  A 
  phe- 
  

   nomenon 
  can 
  there 
  — 
  as 
  well 
  as 
  at 
  a 
  number 
  of 
  other 
  places 
  — 
  be 
  ob- 
  

   served, 
  namely, 
  the 
  disappearance 
  of 
  streams 
  in 
  the 
  morning 
  that 
  may 
  

   have 
  furnished 
  an 
  ample 
  sup])ly 
  of 
  water 
  at 
  any 
  given 
  point 
  during 
  the 
  

   evening 
  preceding. 
  This 
  is 
  due 
  to 
  the 
  cessation 
  of 
  the 
  melting 
  of 
  snow 
  

   that 
  is 
  contained 
  in 
  many 
  crevices 
  in 
  the 
  mountains 
  whereby 
  the 
  creeks 
  

   are 
  fed 
  in 
  the 
  day-time. 
  Farther 
  south, 
  about 
  30 
  miles 
  nortliwest 
  of 
  Fort 
  

   Garland, 
  are 
  the 
  San 
  Luis 
  Lakes, 
  two 
  pouds 
  of 
  considerable 
  extent, 
  but 
  

   little 
  depth, 
  abounding 
  with 
  water-fowl 
  of 
  many 
  species. 
  At 
  their 
  

   shores 
  a 
  plentiful 
  deposit 
  of 
  alkali 
  testifies 
  to 
  the 
  character 
  of 
  the 
  water 
  

   they 
  contain. 
  Going 
  farther 
  south, 
  on 
  the 
  east 
  side, 
  we 
  find 
  streams 
  of 
  

   more 
  importance. 
  The 
  range 
  there 
  becomes 
  wider, 
  and 
  larger 
  volumes 
  

   of 
  water 
  flow 
  into 
  the 
  valley. 
  Ute 
  Creek, 
  Rio 
  Trinchera, 
  Eio 
  Culebra, 
  

   Rio 
  Costilla, 
  and 
  Rio 
  Colorado 
  are 
  of 
  good 
  size, 
  and 
  all 
  oi 
  them 
  

   carry, 
  for 
  a 
  portion 
  of 
  the 
  year 
  at 
  least, 
  water 
  into 
  the 
  Rio 
  Grande. 
  

  

  On 
  the 
  west 
  sideof 
  the 
  valley 
  we 
  observe 
  fewer 
  small 
  creeks, 
  but 
  more 
  

   that 
  retain 
  their 
  water, 
  either 
  during 
  the 
  entire 
  or 
  a 
  large 
  part 
  of 
  the 
  

   year. 
  Saguache 
  Creek 
  is 
  the 
  largest 
  of 
  the 
  more 
  northerly 
  ones, 
  flow- 
  

   ing 
  into 
  San 
  Luis 
  Creek. 
  South 
  of 
  that 
  some 
  small 
  creeks 
  leave 
  Ihe 
  

   mountains, 
  but 
  find 
  an 
  untimely 
  end 
  in 
  the 
  sand. 
  About 
  north 
  latitude, 
  

   37° 
  43', 
  the 
  Rio 
  Grande 
  del 
  ISTorte 
  enters 
  the 
  valley, 
  flowing 
  first 
  in 
  an 
  

   easterly 
  direction, 
  and 
  then, 
  after 
  a 
  run 
  of 
  about 
  45 
  miles, 
  turning 
  south. 
  

   Piedra 
  Pintada, 
  Alamosa, 
  and 
  Conejos 
  are 
  tributaries 
  of 
  the 
  Rio 
  Grande, 
  

   coming 
  from 
  the 
  high 
  volcanic 
  regicn 
  west 
  of 
  the 
  valley. 
  S[)anish 
  set- 
  

   tlements 
  occur 
  all 
  along 
  these 
  latter, 
  as 
  well 
  as 
  on 
  those 
  more 
  southerly 
  

   rivers 
  on 
  the 
  opposite 
  side. 
  A 
  feature 
  of 
  interest 
  may 
  be 
  noticed 
  in 
  

   the 
  courses 
  of 
  the 
  Alamosa 
  and 
  Conejos 
  more 
  ])articularl3% 
  that 
  seems 
  

   sur[u-isiug 
  when 
  the 
  ai)pareut 
  plain 
  through 
  which 
  they 
  flow 
  is 
  taken 
  

   into 
  consideration. 
  Of 
  both 
  these 
  rivers, 
  the 
  course 
  is 
  at 
  first 
  very 
  

   nearly 
  due 
  east, 
  but 
  when 
  they 
  have 
  approached 
  the 
  Rio 
  Grande 
  within 
  

   about 
  10 
  miles, 
  they 
  make 
  a 
  sudden 
  turn 
  to 
  the 
  northeast, 
  and 
  only 
  en- 
  

   ter 
  that 
  river 
  after 
  having 
  flown 
  for 
  some 
  distance 
  in 
  that 
  direction. 
  

   With 
  this 
  the 
  drainage 
  of 
  the 
  San 
  Luis 
  Valley 
  is 
  exhausted, 
  and 
  I 
  shall 
  

   proceed 
  to 
  the 
  consideration 
  of 
  the 
  geological 
  formations 
  surrounding- 
  

   it 
  before 
  e^ntering 
  into 
  the 
  discussion 
  of 
  such 
  features 
  as 
  are 
  shown 
  by 
  the 
  

   valley 
  itself. 
  It 
  is 
  necessary 
  to 
  arrive 
  at 
  a 
  full 
  understanding 
  of 
  all 
  

   points 
  involved 
  before 
  giving 
  those 
  facts 
  that 
  have 
  led 
  to 
  conclusions 
  

   below 
  to 
  be 
  elucidated. 
  

  

  Starting 
  again 
  on 
  the 
  east 
  side 
  from 
  the 
  north, 
  we 
  follow 
  the 
  course 
  

   of 
  the 
  Sangre 
  de 
  Cristo 
  Range,i 
  about 
  15° 
  east 
  of 
  south. 
  Metamor- 
  

   phic 
  rocks 
  compose 
  the 
  northern 
  end, 
  which 
  are 
  soon 
  overlaid, 
  how- 
  

   ever, 
  by 
  sedimentary 
  strata 
  of 
  Carboniferous 
  age. 
  ISTear 
  Mosco 
  Pass 
  

   these 
  strata 
  cover 
  but 
  a 
  small 
  area, 
  and 
  again 
  metamorphic 
  groups 
  

   make 
  their 
  appearance. 
  Sierra 
  Blanca 
  group 
  shows 
  these 
  almost 
  ex- 
  

   clusively. 
  In 
  the 
  Sangre 
  de 
  Cristo 
  Pass, 
  east 
  of 
  Fort 
  Garland, 
  Carbo- 
  

   nilerous 
  is 
  found 
  and 
  continues 
  southward, 
  with 
  some 
  interruptions, 
  

   caused 
  either 
  by 
  superincumbent 
  volcanic 
  rocks 
  or 
  a 
  protrusion 
  of 
  the 
  

   underlying 
  metamorphic 
  material. 
  South 
  of 
  Rio 
  Costilla 
  trachytic 
  

   rocks 
  become 
  predominating, 
  and 
  form 
  the 
  highest 
  portions 
  of 
  the 
  

   range, 
  while 
  metamorphic 
  granite 
  occupies 
  the 
  slopes 
  descending 
  into 
  

   San 
  Luis 
  Valley. 
  iS^orth 
  of 
  this 
  river 
  a 
  basaltic 
  bluff 
  (San 
  Pedro 
  mesa) 
  

  

  