﻿B^a)ucH.] 
  SA 
  WATCH 
  RANGE 
  EIO 
  GRANDE 
  DRAINAGE. 
  153 
  

  

  upper 
  valleys 
  of 
  the 
  streams 
  farther 
  south, 
  after 
  they 
  have 
  left 
  the 
  

   mountains. 
  Almost 
  the 
  entire 
  valleys 
  in 
  question 
  are 
  located 
  in 
  Lower 
  

   Cretaceous 
  beds. 
  In 
  order 
  to 
  facilitate 
  description, 
  the 
  rivers 
  of 
  the 
  

   various 
  regions 
  of 
  the 
  range 
  will 
  be 
  discussed 
  and 
  the 
  variations 
  in 
  

   formations 
  or 
  local 
  phenomena 
  of 
  importance 
  or 
  interest 
  be 
  mentioned. 
  

  

  A. 
  — 
  Eio 
  Grande 
  drainage. 
  

  

  Ascending 
  this 
  river 
  from 
  its 
  entrance 
  into 
  Sau 
  Luis 
  Valley 
  at 
  Del 
  

   Norte 
  and 
  Loma, 
  we 
  find 
  trachytic 
  formations 
  on 
  either 
  side. 
  North 
  of 
  

   the 
  river 
  the 
  bluffs 
  gradually 
  decrease 
  in 
  height 
  as 
  they 
  approach 
  the 
  

   valley. 
  Trachyte, 
  or 
  a 
  conglomerate 
  composed 
  of 
  trachytic 
  material, 
  

   forms 
  them. 
  A 
  decided 
  dip 
  eastward 
  of 
  3° 
  to 
  6° 
  is 
  noticeable 
  in 
  the 
  

   strata 
  or 
  flows, 
  and 
  on 
  that 
  side 
  the 
  bluffs 
  slope 
  into 
  the 
  intervening 
  

   valleys 
  and 
  into 
  San 
  Luis 
  gently, 
  without 
  many 
  breaks. 
  Facing 
  them 
  

   from 
  the 
  west, 
  however, 
  this 
  is 
  changed. 
  A 
  sketch 
  made 
  from 
  station 
  

   11, 
  looking 
  east, 
  is 
  here 
  given, 
  which 
  illustrates 
  the 
  character 
  of 
  the 
  

   bluffs. 
  On 
  the 
  west 
  side 
  steep, 
  vertical 
  walls 
  of 
  the 
  brown 
  trachyte 
  are 
  

   presented 
  near 
  the 
  summits 
  of 
  the 
  hills, 
  some 
  of 
  them 
  showing 
  preci- 
  

   pices 
  a 
  thousand 
  feet 
  in 
  height. 
  These 
  walls, 
  inaccessible 
  from 
  the 
  west, 
  

   except 
  where 
  a 
  break 
  may 
  occur, 
  often 
  stretch 
  for 
  considerable 
  distance 
  

   in 
  the 
  direction 
  north 
  to 
  south. 
  Small 
  caves 
  and 
  arches 
  are 
  formed 
  by 
  

   erosion 
  and 
  decomposition 
  in 
  them, 
  and 
  the 
  debris 
  from 
  their 
  faces 
  

   covers 
  the 
  narrow 
  valleys 
  in 
  between. 
  Covered 
  by 
  piiions 
  and 
  cedars, 
  

   they 
  sometimes 
  still 
  show 
  grassy 
  slopes 
  that 
  prove 
  to 
  be 
  an 
  acceptable 
  

   pasture 
  for 
  the 
  sheep-herds 
  of 
  the 
  neighboring 
  settlers. 
  Owing 
  to 
  the 
  

   loose 
  nature 
  of 
  the 
  soil 
  and 
  gravel 
  in 
  the 
  valleys, 
  water 
  is 
  at 
  certain 
  

   seasons 
  of 
  the 
  year 
  rarely 
  to 
  be 
  found. 
  Springs 
  occur 
  near 
  the 
  bases 
  

   of 
  some 
  of 
  the 
  bluffs, 
  but 
  run 
  only 
  a 
  short 
  distance. 
  Combiued 
  with 
  

   the 
  easterly 
  dip 
  is 
  ones 
  toward 
  the 
  south, 
  ijroduced 
  by 
  a 
  concave 
  curva- 
  

   ture 
  of 
  the 
  volcanic 
  strata. 
  This 
  latter 
  is 
  at 
  right-angles 
  to 
  the 
  course 
  

   of 
  the 
  river 
  ; 
  its 
  strike 
  therefore 
  is 
  parallel 
  with 
  it. 
  Correspondingly 
  

   we 
  find 
  a 
  northerly 
  dip 
  south 
  of 
  the 
  Rio 
  Grande. 
  Thus 
  a 
  shallow 
  

   synclinal 
  fold 
  is 
  formed, 
  in 
  the 
  axis 
  of 
  which 
  the 
  river 
  finds 
  its 
  

   course. 
  This 
  accounts 
  for 
  the 
  almost 
  straight 
  line 
  followed 
  by 
  it 
  

   for 
  nearly 
  fifteen 
  miles. 
  Comparing 
  the 
  trachytic 
  strata 
  of 
  this 
  vicinity 
  

   with 
  those 
  farther 
  west 
  in 
  the 
  mountains, 
  it 
  will 
  be 
  found 
  that 
  they 
  cor- 
  

   respond 
  with 
  No. 
  3, 
  though 
  they 
  appear 
  to 
  have 
  lost 
  in 
  thickness. 
  Sta- 
  

   tion 
  11 
  is 
  10,460 
  feet 
  high, 
  while 
  Del 
  Norte, 
  nearly 
  due 
  south 
  of 
  it, 
  is 
  

   about 
  8,000 
  feet 
  above 
  sea-level. 
  Farther 
  toward 
  the 
  northwest 
  the 
  

   mountains 
  get 
  higher, 
  so 
  that 
  station 
  26 
  is 
  located 
  at 
  an 
  elevation 
  of 
  

   13,711 
  feet. 
  Here 
  the 
  character 
  of 
  the 
  volcanic 
  rocks 
  corresponds 
  

   closely 
  to 
  that 
  observed 
  in 
  the 
  1874 
  district. 
  

  

  Following 
  up 
  the 
  river 
  we 
  pass 
  station 
  56 
  of 
  1874, 
  which 
  is 
  located 
  on 
  an 
  

   isolated 
  outcrop 
  of 
  blue 
  Carboniferous 
  sandstone. 
  So 
  far 
  as 
  could 
  be 
  

   determined, 
  there 
  are 
  several 
  disconnected 
  outcrops 
  of 
  the 
  same 
  rock 
  

   on 
  either 
  side 
  of 
  the 
  Eio 
  Grande. 
  They 
  have 
  probably 
  been 
  brought 
  

   "to 
  day" 
  by 
  denudation. 
  Trachyte 
  surrounds 
  them 
  on 
  all 
  sides, 
  and 
  

   covers 
  their 
  extension 
  toward 
  the 
  south. 
  It 
  was 
  expected 
  that 
  their 
  

   continuation 
  would 
  be 
  found 
  on 
  the 
  western 
  edge 
  of 
  the 
  volcanic 
  area, 
  

   but 
  this 
  was 
  not 
  verified. 
  Although 
  the 
  outcrops 
  are 
  very 
  small, 
  occur- 
  

   ring 
  merely 
  along 
  the 
  lower 
  ridge, 
  running 
  parallel 
  with 
  the 
  river, 
  they 
  

   are 
  sufficiently 
  characteristic 
  to 
  admit 
  of 
  recognition. 
  This 
  is 
  the 
  only 
  

   instance 
  where, 
  in 
  the 
  volcanic 
  district 
  of 
  1875, 
  unchanged 
  sedimentary 
  

   beds 
  were 
  found 
  protruding 
  through 
  the 
  superincumbent 
  trachytic 
  

   beds. 
  It 
  argues, 
  inasmuch 
  as 
  the 
  case 
  is 
  so 
  isolated, 
  for 
  the 
  as- 
  

  

  