﻿TOPOGRAPHICAL 
  REPORT 
  ON 
  THE 
  SAN 
  JPAN 
  DIS- 
  

   TRICT. 
  

  

  The 
  area 
  of 
  country 
  assigned 
  to 
  me 
  for 
  topographical 
  work 
  in 
  1874 
  

   consisted 
  of 
  two 
  distinct 
  districts, 
  the 
  first 
  a 
  narrow 
  belt 
  of 
  the 
  plains 
  and 
  

   "hogbacks" 
  on 
  the 
  eastern 
  edge 
  of 
  sheet 
  No. 
  83, 
  and 
  the 
  second 
  and 
  

   main 
  portion 
  an 
  area 
  in 
  Southwestern 
  Colorado 
  from 
  108° 
  west 
  longi- 
  

   tude 
  to 
  1090 
  30', 
  and 
  between 
  36° 
  45' 
  and 
  37° 
  51' 
  north 
  latitude. 
  These 
  

   boundaries 
  carried 
  the 
  work 
  15' 
  into 
  New 
  Mexico 
  and 
  30' 
  into 
  Utah, 
  

   with 
  a 
  rectangle 
  15' 
  by 
  30' 
  in 
  Arizona. 
  

  

  The 
  first 
  district 
  lay 
  west 
  of 
  104° 
  30' 
  west 
  longitude, 
  and 
  principally 
  

   between 
  that 
  and 
  104° 
  50', 
  its 
  southern 
  limit 
  being 
  38° 
  00' 
  and 
  its 
  

   northern 
  limit 
  39° 
  15' 
  north 
  latitude. 
  The 
  two 
  districts 
  combined 
  con- 
  

   tained 
  about 
  7,000 
  square 
  miles. 
  

  

  The 
  southwestern 
  or 
  main 
  portion 
  lying 
  some 
  three 
  weeks' 
  march 
  

   from 
  Denver 
  (our 
  base 
  of 
  supplies,) 
  and 
  the 
  strip 
  of 
  plains 
  being 
  directly 
  

   in 
  the 
  course, 
  it 
  was 
  determined 
  to 
  work 
  this 
  field 
  on 
  the 
  outward 
  

   march 
  and 
  leave 
  nothing 
  unfinished 
  for 
  the 
  uncertain 
  weather 
  of 
  the 
  

   fall. 
  This 
  precaution 
  proved 
  to 
  have 
  been 
  wise, 
  since 
  unlooked-for 
  

   complications 
  in 
  the 
  summer 
  would 
  have 
  rendered 
  the 
  working 
  of 
  this 
  

   area 
  at 
  the 
  close 
  of 
  the 
  season 
  almost 
  impossible. 
  

  

  Since 
  all 
  that 
  portion 
  of 
  sheet 
  No. 
  83 
  outside 
  of 
  the 
  granite 
  mountain- 
  

   mass 
  has 
  been 
  worked 
  by 
  myself 
  within 
  the 
  last 
  two 
  years, 
  I 
  shall 
  

   consider 
  here 
  the 
  plains 
  and 
  connecting 
  topography 
  to 
  the 
  foot-hills 
  ; 
  

   it 
  being 
  characteristic 
  of 
  the 
  whole 
  eastern 
  base 
  of 
  the 
  Eocky 
  Mount- 
  

   ain 
  system. 
  

  

  The 
  plains 
  sloping 
  up 
  from 
  the 
  Mississippi 
  and 
  Missouri 
  Elvers 
  with 
  

   an 
  extremely 
  gentle 
  rise, 
  have 
  only 
  local 
  disturbances 
  of 
  their 
  generally 
  

   flat 
  and 
  slightly 
  rolling 
  character, 
  and 
  are 
  only 
  cut 
  by 
  the 
  main 
  great 
  

   rivers, 
  as 
  the 
  Arkansas, 
  Platte, 
  and 
  their 
  principal 
  branches, 
  but 
  as 
  the 
  

   mountains 
  are 
  neared 
  the 
  plains 
  in 
  many 
  cases 
  feel 
  the 
  influence 
  of 
  

   the 
  mountain's 
  upheaval 
  and 
  show 
  greater 
  evidence 
  of 
  recent 
  erosion, 
  

   so 
  that 
  for 
  ten 
  and 
  even 
  twenty 
  or 
  more 
  miles 
  from 
  the 
  actual 
  mount- 
  

   ain-base 
  we 
  find 
  broken, 
  low 
  plateaus, 
  isolated 
  buttes, 
  and 
  quite 
  

   marked 
  ranges 
  of 
  hills 
  and 
  deep 
  valley 
  depressions. 
  The 
  numerous 
  

   mountain-streams 
  too, 
  which 
  here 
  flow 
  out 
  through 
  the 
  plains 
  at 
  

   almost 
  every 
  mile, 
  add 
  to 
  the 
  detail 
  of 
  this 
  peculiar 
  topography. 
  

  

  The 
  small 
  detail 
  of 
  much 
  of 
  this 
  topography 
  and 
  the 
  slight 
  range 
  of 
  

   altitude 
  before 
  the 
  mountains 
  are 
  reached 
  render 
  a 
  good 
  expression 
  of 
  

   it 
  in 
  our 
  adopted 
  scale 
  of 
  200- 
  foot 
  contours 
  often 
  impossible, 
  and 
  in 
  the 
  

   plotted 
  map 
  I 
  can 
  only 
  hope 
  to 
  give 
  a 
  general 
  idea 
  of 
  its 
  change 
  in 
  

   character. 
  In 
  the 
  higher 
  mountain 
  portions 
  of 
  Colorado 
  200foot 
  con- 
  

   tours, 
  at 
  our 
  scale 
  of 
  4 
  miles 
  to 
  an 
  inch, 
  often 
  become 
  almost 
  unmanage- 
  

   able 
  from 
  their 
  closeness. 
  It 
  seems 
  unadvisable 
  to 
  interpolate 
  for 
  the 
  

   low 
  country 
  ; 
  we 
  were, 
  therefore, 
  obliged 
  to 
  satisfy 
  ourselves 
  with 
  the 
  

   best 
  results 
  attainable 
  with 
  this 
  wide 
  range 
  of 
  height 
  between 
  our 
  hori- 
  

   zontal 
  planes. 
  The 
  whole 
  face 
  of 
  the 
  Eocky 
  Mountains 
  rises 
  with 
  great 
  

   abruptness 
  from 
  the 
  plains, 
  marking 
  with 
  all 
  its 
  bays 
  and 
  outstanding 
  

   points 
  a 
  clearly-defined 
  shore-line 
  to 
  the 
  greater 
  prairie-sea 
  to 
  the 
  east- 
  

   ward. 
  The 
  general 
  trend 
  of 
  the 
  mountain-base 
  in 
  Colorado 
  is 
  a 
  little 
  

  

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