﻿TOPOGRAPHICAL 
  REPORT 
  OxN 
  THE 
  GRAND 
  RIVER 
  

  

  DISTRICT. 
  

  

  The 
  area 
  assigned 
  to 
  the 
  division 
  under 
  my 
  charge 
  for 
  the 
  field-seasons 
  

   of 
  1875 
  and 
  1876 
  comprised 
  about 
  10,000 
  square 
  miles. 
  Its 
  limits 
  were 
  as 
  

   follows 
  : 
  Commencing 
  at 
  the 
  intersection 
  of 
  the 
  parallel 
  of 
  latitude 
  of 
  

   39° 
  30' 
  with 
  the 
  meridian 
  109° 
  30', 
  the 
  north 
  line 
  runs 
  east 
  along 
  the 
  par- 
  

   allel 
  39° 
  30' 
  to 
  its 
  intersection 
  with 
  the 
  Grand 
  Eiver 
  in 
  longitude 
  

   108° 
  08'. 
  Thence 
  it 
  follows 
  down 
  the 
  Grand 
  to 
  the 
  mouth 
  of 
  the 
  Gunni- 
  

   son, 
  up 
  the 
  Gunnison 
  to 
  the 
  mouth 
  of 
  Lake 
  Fork, 
  up 
  this 
  latter 
  stream 
  

   to 
  the 
  northern 
  edge 
  of 
  the 
  San 
  Juan 
  Mountains, 
  and 
  follows 
  this 
  edge 
  

   westward 
  to 
  the 
  end 
  of 
  the 
  range 
  ; 
  thence 
  it 
  follows 
  the 
  parallel 
  of 
  

   37° 
  52' 
  westward 
  to 
  the 
  meridian 
  109° 
  30', 
  which 
  meridian 
  forms 
  the 
  

   western 
  limit 
  of 
  the 
  ^ork. 
  

  

  In 
  the 
  prosecution 
  of 
  the 
  work 
  130 
  topographical 
  stations 
  were 
  made, 
  

   an 
  average 
  of 
  one 
  in 
  every 
  77 
  square 
  miles. 
  This 
  area 
  is 
  mainly 
  made* 
  

   up 
  of 
  plateaus 
  considerably 
  disturbed 
  by 
  the 
  same 
  forces 
  which 
  have 
  

   elevated 
  the 
  great 
  ranges 
  farther 
  east. 
  It 
  is 
  drained 
  by 
  the 
  Grand, 
  

   Gunnison, 
  Uncompahgre, 
  Dolores, 
  and 
  San 
  Miguel 
  Elvers. 
  

  

  The 
  remarkable 
  parallelism 
  of 
  the 
  separate 
  ranges 
  which 
  make 
  up 
  

   the 
  mountain 
  system 
  of 
  Colorado 
  has 
  been 
  previously 
  noticed 
  in 
  the 
  

   reports 
  of 
  this 
  survey. 
  Their 
  trends 
  are 
  all 
  between 
  southeast 
  and 
  

   south, 
  while 
  the 
  ruling 
  trend 
  is 
  about 
  south-southeast. 
  This 
  I 
  call, 
  for 
  

   convenience, 
  the 
  normal 
  trend. 
  The 
  Front, 
  Park, 
  Sangre 
  de 
  Cristo, 
  

   Sa 
  watch, 
  San 
  Juan, 
  and 
  Elk 
  ranges, 
  with 
  their 
  inclosed 
  valleys, 
  all 
  

   trend 
  in 
  this 
  direction. 
  Almost 
  every 
  one 
  of 
  the 
  secondary 
  streams 
  bf 
  

   the 
  State 
  conform 
  to 
  this 
  normal 
  course. 
  

  

  West 
  of 
  the 
  Elk 
  ranges 
  lies 
  the 
  district 
  under 
  consideration, 
  and 
  

   here 
  the 
  same 
  conditions 
  prevail; 
  but 
  instead 
  of 
  mountain 
  ranges 
  there 
  

   are 
  long 
  inclined 
  plateaus, 
  low, 
  hogback-like 
  ridges 
  and 
  cailons. 
  There 
  

   is, 
  first, 
  the 
  valley 
  of 
  the 
  Uncompahgre, 
  which 
  extends 
  down 
  that 
  river 
  

   35 
  miles, 
  then 
  down 
  the 
  Gunnison 
  about 
  the 
  same 
  distance 
  to 
  its 
  mouth, 
  

   and 
  thence 
  down 
  the 
  Gr-and 
  40 
  or 
  50 
  miles, 
  with 
  a 
  general 
  course 
  to 
  the 
  

   northwest, 
  but 
  bending 
  around 
  more 
  to 
  the 
  west 
  on 
  Grand 
  Eiver. 
  

   West 
  of 
  the 
  valley 
  and 
  parallel 
  to 
  it 
  is 
  an 
  inclined 
  plateau, 
  the 
  

   Uncompahgre 
  Plateau, 
  sloping 
  toward 
  the 
  northeast 
  very 
  gently, 
  and 
  

   breaking 
  off 
  abruptly 
  to 
  the 
  southwest. 
  Its 
  crest 
  extends 
  from 
  the 
  foot 
  

   of 
  the 
  San 
  Juan 
  Mountains 
  to 
  the 
  head 
  of 
  the 
  bend 
  of 
  the 
  Grand. 
  Its 
  

   mean 
  height 
  above 
  the 
  valley 
  at 
  the 
  mouth 
  of 
  the 
  Uncompahgre 
  is 
  4,000 
  

   feet, 
  or 
  about 
  9,000 
  feet 
  above 
  the 
  sea. 
  West 
  of 
  this 
  is 
  the 
  Eio 
  San 
  

   Miguel, 
  in 
  a 
  close 
  caiion, 
  with 
  a 
  northwest 
  course 
  from 
  its 
  head 
  to 
  its 
  

   mouth. 
  Then 
  a 
  succession 
  of 
  ridges 
  and 
  valleys 
  is 
  met 
  with, 
  all 
  having 
  

   the 
  same 
  northwest 
  trend. 
  North 
  of 
  them 
  rises 
  the 
  group 
  known 
  as 
  the 
  

   Sierra 
  la 
  Sal, 
  of 
  igneous 
  origin, 
  and 
  of 
  later 
  date 
  than 
  these 
  ridges, 
  as 
  

   the 
  latter 
  are 
  carried 
  up 
  on 
  their 
  slopes. 
  

  

  The 
  Eio 
  Dolores 
  enters 
  this 
  district 
  from 
  the 
  south, 
  with 
  a 
  course 
  

   about 
  north-northwest, 
  in 
  heavy 
  caQou 
  in 
  the 
  " 
  Great 
  Sage-plain 
  '' 
  of 
  

  

  337 
  

   22 
  G 
  S 
  

  

  