﻿ENDUCH.J 
  SAN 
  LUIS 
  VALLEY 
  — 
  FORMER 
  LAKES. 
  147 
  

  

  leaving 
  the 
  mountaias, 
  the 
  river 
  suddenly 
  bends 
  to 
  the 
  northeast 
  and 
  

   joins 
  the 
  Grande 
  north 
  of 
  the 
  trachytic 
  and 
  basaltic 
  group. 
  Being- 
  

   forced 
  to 
  abandon 
  its 
  flow 
  toward 
  the 
  east 
  by 
  the 
  dip 
  of 
  the 
  volcanic 
  

   strata, 
  and 
  being 
  prevented 
  from 
  turning 
  south 
  by 
  the 
  northeasterly 
  

   dip 
  of 
  the 
  basalt 
  through 
  which 
  it 
  had 
  flown 
  down, 
  the 
  only 
  course 
  

   remaining 
  open 
  was 
  that 
  to 
  the 
  northeast. 
  A 
  glance 
  at 
  the 
  map 
  will 
  

   show 
  the 
  curious 
  course 
  of 
  the 
  river, 
  while 
  but 
  eight 
  miles 
  distant 
  from 
  

   it 
  the 
  Rio 
  Grande 
  flows 
  in 
  precisely 
  the 
  opposite 
  direction. 
  A 
  caiion 
  in 
  

   which 
  the 
  Rio 
  Grande 
  flows 
  has 
  been 
  alluded 
  to 
  above, 
  and 
  the 
  same 
  

   origin 
  has 
  been 
  claimed 
  for 
  it 
  as 
  for 
  that 
  of 
  the 
  San 
  Antonio. 
  Judging 
  

   from 
  the 
  direction 
  of 
  the 
  cracks 
  and 
  canons 
  in 
  the 
  basalt, 
  it 
  may 
  be 
  in- 
  

   ferred 
  that 
  the 
  seismic 
  action 
  originated 
  in 
  the 
  immediate 
  vicinity 
  of 
  

   Ute 
  Peak. 
  Evidences 
  of 
  former 
  river-courses 
  are 
  to 
  be 
  found 
  near 
  the 
  

   Rio 
  Grande 
  and 
  near 
  the 
  Culebra. 
  This 
  led 
  to 
  a 
  more 
  careful 
  investi- 
  

   gation 
  of 
  the 
  previous 
  condition 
  of 
  that 
  as 
  well 
  as 
  the 
  remaining 
  por- 
  

   tions 
  of 
  San 
  Luis 
  Valley. 
  Although 
  the 
  results 
  obtained 
  might 
  have 
  

   been 
  presented 
  in 
  more 
  detail 
  and 
  with 
  more 
  accuracy 
  had 
  time 
  per- 
  

   mitted, 
  I 
  trust 
  that 
  at 
  some 
  future 
  time 
  we 
  may 
  be 
  able 
  to 
  verify 
  them 
  

   by 
  means 
  of 
  surveys 
  on 
  such 
  a 
  scale 
  as 
  to 
  leave 
  no 
  room 
  for 
  doubt. 
  

  

  Regarding 
  the 
  physical 
  condition 
  of 
  the 
  surface 
  of 
  San 
  Luis 
  Valley, 
  

   it 
  can 
  appropriately 
  be 
  divided 
  into 
  three 
  groups: 
  1, 
  the 
  fine 
  sand- 
  

   drift 
  ; 
  2, 
  the 
  local 
  drift 
  along 
  the 
  edges 
  of 
  the 
  valley 
  ; 
  and, 
  3, 
  that 
  area 
  

   upon 
  which 
  basalt 
  is 
  exposed. 
  Of 
  the 
  first 
  group 
  we 
  find 
  two 
  large 
  

   areas 
  ; 
  the 
  northern 
  one 
  commencing 
  north 
  of 
  San 
  Luis 
  lakes, 
  extend- 
  

   ing 
  both 
  east 
  and 
  west, 
  to 
  within 
  a 
  short 
  distance 
  of 
  the 
  inclosing 
  

   ranges, 
  and 
  finding 
  its 
  southern 
  terminus 
  a 
  short 
  distance 
  below 
  the 
  

   junction 
  of 
  the 
  Conejos 
  with 
  the 
  Rio 
  Grande. 
  From 
  there 
  it 
  extends 
  

   eastward 
  and 
  connects, 
  about 
  fourteen 
  miles 
  west 
  of 
  station 
  105, 
  with 
  

   the 
  southern 
  sand-drift 
  region. 
  This 
  fills 
  the 
  flat 
  valley 
  lying 
  between 
  

   the 
  San 
  Pedro 
  mesa 
  and 
  the 
  plateau 
  of 
  station 
  104. 
  It 
  ends 
  about 
  

   eight 
  miles 
  below 
  Ute 
  Peak. 
  Of 
  the 
  second 
  group 
  but 
  little 
  needs 
  be 
  

   said, 
  as 
  it 
  is 
  determined 
  by 
  the 
  number 
  and 
  rapidity 
  of 
  mountain- 
  

   streams 
  that 
  may 
  be 
  found 
  all 
  along 
  the 
  edge 
  of 
  the 
  valley. 
  Basalt, 
  as 
  

   already 
  stated, 
  has 
  produced 
  but 
  little 
  soil 
  in 
  the 
  valley, 
  save 
  in 
  the 
  im- 
  

   mediate 
  neighborhood 
  of 
  streams. 
  It 
  is 
  covered 
  by 
  sand 
  at 
  all 
  those 
  

   points 
  where 
  the 
  two 
  meet. 
  

  

  Judging 
  from 
  the 
  evident 
  deflection 
  of 
  rivers, 
  the 
  failure 
  of 
  mount- 
  

   ain-streams 
  to 
  carry 
  specimens 
  of 
  the 
  rocks 
  through 
  which 
  they 
  pass 
  

   into 
  the 
  valley 
  for 
  any 
  distance, 
  the 
  deposition 
  in 
  banks 
  of 
  the 
  ma- 
  

   terial 
  that 
  many 
  streams 
  bring 
  with 
  them, 
  and 
  the 
  cafioned 
  outlet 
  of 
  the 
  

   Rio 
  Grande, 
  I 
  have 
  come 
  to 
  the 
  conclusion 
  that 
  at 
  one 
  time 
  San 
  Luis 
  

   Valley 
  was 
  covered 
  by 
  two 
  large 
  lakes, 
  the 
  northern 
  and 
  the 
  southern. 
  

   These 
  I 
  have 
  named, 
  in 
  order 
  to 
  facilitate 
  discussion, 
  Oorouado's 
  Lakes. 
  

   Of 
  these 
  the 
  former 
  covered 
  about 
  1,400 
  square 
  miles 
  ; 
  the 
  latter 
  300 
  

   square 
  miles. 
  I 
  have 
  alluded 
  to 
  the 
  caiion 
  near 
  station 
  105, 
  cut 
  

   through 
  the 
  trachyte. 
  It 
  is 
  about 
  three 
  miles 
  in 
  length, 
  and 
  its 
  

   general 
  direction 
  is 
  perfectly 
  straight. 
  In 
  case 
  that 
  narrow 
  passage, 
  

   which 
  I 
  assume 
  to 
  have 
  been 
  opened 
  by 
  seismic 
  force, 
  should 
  be 
  closed 
  

   to-day, 
  the 
  result 
  would 
  be 
  an 
  accumulation 
  of 
  water 
  in 
  the 
  northern 
  

   half 
  of 
  San 
  Luis 
  Valley, 
  the 
  formation 
  of 
  a 
  lake. 
  This 
  lake 
  would 
  

   reach 
  a 
  certain 
  depth 
  of 
  water, 
  consequently 
  increase 
  in 
  area 
  until 
  the 
  

   slight 
  rise 
  southwest 
  of 
  Fort 
  Garland 
  would 
  be 
  overcome, 
  and 
  it 
  would 
  

   then 
  flow 
  over 
  into 
  the 
  southern 
  region 
  of 
  the 
  sand-drift, 
  the 
  lowest 
  

   portion 
  of 
  the 
  valley 
  there. 
  No 
  outlet 
  would 
  be 
  formed 
  on 
  the 
  western 
  

   side 
  of 
  San 
  Luis 
  Valley, 
  on 
  account 
  of 
  the 
  rise 
  produced 
  by 
  the 
  dipping 
  

   (northeast) 
  of 
  the 
  basalt 
  strata. 
  It 
  seems 
  ta 
  me 
  that 
  the 
  presence 
  of 
  

  

  