﻿160 
  REPORT 
  UNITED 
  STATES 
  GEOLOGICAL 
  SURVEY. 
  

  

  lope 
  Park, 
  are 
  a 
  series 
  of 
  bluifs, 
  upon 
  one 
  of 
  which 
  station 
  53 
  of 
  1874 
  was 
  

   located, 
  at 
  an 
  elevation 
  of 
  10,303 
  feet. 
  With 
  great 
  certainty 
  the 
  strata 
  

   of 
  trachyte 
  No. 
  2 
  and 
  No. 
  3 
  can 
  be 
  separated 
  here. 
  They 
  are 
  very 
  

   nearly 
  horizontal, 
  having 
  but 
  a 
  slight 
  dip 
  to 
  the 
  eastward. 
  There 
  is 
  no 
  

   doubt 
  that 
  the 
  bluffs, 
  now 
  separated 
  by 
  canons, 
  were 
  at 
  one 
  time 
  a 
  con- 
  

   tinuous 
  plain, 
  over 
  which 
  the 
  Eio 
  Grande 
  may 
  have 
  found 
  its 
  course. 
  

   In 
  that 
  case 
  the 
  deposition 
  of 
  erratic 
  material 
  near 
  stations 
  33 
  and 
  34 
  

   would 
  be 
  fully 
  explained, 
  but 
  there 
  is 
  no 
  sufficient 
  proof 
  at 
  hand 
  to 
  sub- 
  

   stantiate 
  the 
  supposition, 
  although 
  it 
  is 
  the 
  only 
  one 
  affording 
  a 
  sem- 
  

   blance 
  of 
  probability. 
  The 
  caQon 
  opposite 
  station 
  53 
  of 
  1874, 
  through 
  

   which 
  the 
  river 
  flows, 
  is 
  one 
  of 
  separation, 
  not 
  of 
  erosion, 
  as 
  is 
  amply 
  

   shown 
  by 
  the 
  cbaracterof 
  its 
  walls, 
  by 
  its 
  course, 
  and 
  by 
  its 
  topographical 
  

   features 
  generally. 
  As 
  such 
  is 
  the 
  case, 
  the 
  chasm 
  produced 
  would 
  

   have 
  afforded 
  a 
  convenient 
  outlet 
  for 
  the 
  river 
  into 
  the 
  lower 
  country 
  

   east 
  of 
  Antelope 
  Park, 
  and 
  abandoning 
  the 
  elevated 
  position 
  heretofore 
  

   occupied, 
  the 
  Rio 
  Grande 
  would 
  have 
  sunk 
  its 
  level 
  nearly 
  a 
  thousand 
  

   feet. 
  Just 
  above 
  the 
  canon 
  the 
  creek 
  flowing 
  north 
  from 
  Weeminuche 
  

   Pass 
  enters 
  the 
  river, 
  and 
  there 
  the 
  work 
  of 
  1875 
  joins 
  with 
  that 
  of 
  1874. 
  

  

  All 
  the 
  drainage 
  flowing 
  into 
  the 
  Eio 
  Grande 
  from 
  the 
  south, 
  runs 
  

   entirely 
  in 
  trachyte, 
  until 
  we 
  reach 
  those 
  streams 
  that 
  flow 
  for 
  some 
  

   distance 
  through 
  San 
  Luis 
  Valley 
  before 
  joining 
  the 
  river. 
  Of 
  the 
  

   former, 
  the 
  south 
  Eio 
  Grande 
  is 
  the 
  most 
  prominent. 
  It 
  heads 
  south 
  of 
  

   station 
  18, 
  flows 
  first 
  west 
  of 
  north, 
  then 
  takes 
  a 
  turn 
  toward 
  the 
  east. 
  

   Trachyte 
  No. 
  3, 
  and 
  high 
  up 
  in 
  the 
  mountains 
  No. 
  4, 
  occur 
  within 
  the 
  

   limits 
  of 
  its 
  drainage. 
  In 
  lithological 
  character 
  the 
  strata 
  here 
  are 
  

   identical 
  with 
  their 
  western 
  continuations 
  in 
  the 
  Uucompabgre 
  group. 
  

   No. 
  4 
  is 
  not 
  developed 
  to 
  so 
  great 
  a 
  thickness 
  as 
  there, 
  and 
  in 
  conse- 
  

   quence 
  the 
  peaks 
  do 
  not 
  reach 
  the 
  high 
  elevations 
  that 
  we 
  find 
  farther 
  

   west. 
  Station 
  21, 
  near 
  the 
  headwaters 
  of 
  this 
  stream, 
  on 
  the 
  continental 
  

   divide, 
  has 
  an 
  elevation 
  of 
  13,323 
  feet, 
  and 
  station 
  28, 
  at 
  the 
  head 
  of 
  

   Hot 
  Springs 
  Creek, 
  is 
  13,160 
  feet 
  high. 
  This 
  may 
  be 
  regarded 
  as 
  an 
  

   average 
  for 
  the 
  higher 
  peaks 
  of 
  the 
  plateau-range 
  upon 
  which 
  they 
  

   occur. 
  More 
  elevated 
  mountains 
  are 
  not 
  wanting 
  in 
  the 
  range, 
  but 
  

   they 
  are 
  not 
  numerous. 
  Strati 
  graphically 
  the 
  conditions 
  are 
  very 
  sim- 
  

   ple^ 
  a 
  gentle, 
  general 
  easterly 
  dip 
  being 
  the 
  only 
  variation 
  from 
  the 
  

   horizontal 
  noticeable, 
  with 
  the 
  exception 
  of 
  some 
  slight 
  local 
  faults 
  or 
  

   of 
  " 
  drops." 
  From 
  station 
  20, 
  (11,892 
  feet,) 
  one 
  of 
  the 
  former 
  was 
  

   noticed 
  in 
  a 
  bluff 
  to 
  the 
  northeast. 
  On 
  the 
  face 
  of 
  the 
  plateau-like 
  

   bluff 
  a 
  dark 
  stratum 
  of 
  trachyte 
  is 
  exposed, 
  which 
  has 
  been 
  displaced 
  

   for 
  the 
  vertical 
  distance 
  of 
  about 
  200 
  feet. 
  The 
  line 
  of 
  the 
  fault 
  break- 
  

   age 
  is 
  marked 
  very 
  prominently 
  by 
  the 
  debris 
  of 
  the 
  dark 
  bed. 
  Most 
  

   of 
  the 
  ridges 
  in 
  this 
  locality 
  partake 
  of 
  the 
  characters 
  of 
  plateaus, 
  sep- 
  

   arated 
  by 
  deep 
  canons. 
  

  

  Below 
  the 
  South 
  Rio 
  Grande, 
  the 
  next 
  stream 
  of 
  importance 
  is 
  the 
  

   San 
  Francisco. 
  It 
  flows 
  mainly 
  through 
  trachytic 
  strata, 
  but 
  enters 
  

   San 
  Luis 
  Valley 
  near 
  Del 
  Norte. 
  Near 
  its 
  headwaters 
  stations 
  17 
  and 
  

   18 
  are 
  located, 
  the 
  latter 
  12,768 
  feet 
  above 
  sea-level. 
  They 
  are 
  within 
  

   the 
  vSummit 
  mining 
  district, 
  the 
  discovery 
  of 
  which 
  created 
  considerable 
  

   excitement 
  several 
  years 
  ago. 
  In 
  this 
  district 
  we 
  find 
  the 
  " 
  red 
  stratum 
  "* 
  

   developed, 
  that 
  is 
  an 
  important 
  feature 
  in 
  the 
  mining 
  regions 
  of 
  the 
  San 
  

   Juan 
  country. 
  Here, 
  as 
  there, 
  the 
  color 
  is 
  produced 
  by 
  the 
  decomposi- 
  

   tion 
  of 
  very 
  minute 
  pyrite 
  crystals, 
  with 
  which 
  the 
  trachyte 
  is 
  thor- 
  

   oughly 
  impregnated. 
  Inasmuch 
  as 
  it 
  denotes 
  the 
  presence 
  of 
  a 
  mineral 
  

   that 
  very 
  frequently 
  is 
  auriferous, 
  the 
  appearance 
  of 
  this 
  characteristic 
  

  

  * 
  Report 
  United 
  States 
  Geological 
  Survey 
  1874, 
  p. 
  197. 
  

  

  