﻿434 
  REPORT- 
  UNITED 
  STATES 
  GEOLOGICAL 
  SURVEY. 
  

  

  from 
  10 
  miles 
  nortli 
  of 
  Arapaho 
  Peaks 
  northward 
  to 
  nearly 
  40° 
  30' 
  

   latitude. 
  With 
  two 
  exceptions, 
  the 
  spurs 
  toward 
  east 
  assume, 
  after 
  

   their 
  separation 
  from 
  the 
  main 
  range, 
  either 
  a 
  very 
  moderately 
  rounded 
  

   form, 
  or 
  in 
  most 
  cases 
  that 
  depressed 
  bulky 
  and 
  broad 
  character 
  which 
  

   we 
  generally 
  observe 
  in 
  mountains 
  destined 
  to 
  be 
  soon 
  absorbed 
  by 
  a 
  

   lower 
  country. 
  

  

  We 
  might 
  regard 
  the 
  crest 
  of 
  the 
  main 
  range 
  as 
  about 
  18 
  miles 
  dis- 
  

   tant 
  from 
  the 
  foot-hills. 
  Two-thirds 
  of 
  this 
  intervening 
  space 
  are 
  oc- 
  

   cuijied 
  by 
  mountains 
  of 
  subordinate 
  order 
  and 
  totally 
  different 
  in 
  char- 
  

   acter 
  to 
  what 
  we 
  are 
  used 
  to 
  observe 
  along 
  the 
  rest 
  of 
  the 
  eastern 
  

   slope 
  for 
  hundreds 
  of 
  miles. 
  In 
  the 
  most 
  northern 
  parts 
  of 
  the 
  Eocky 
  

   Mountains, 
  between 
  parallels 
  46° 
  and 
  48°, 
  1 
  had 
  occasion 
  to 
  observe 
  

   here 
  and 
  there 
  clusters 
  and 
  mountain 
  groups 
  lying 
  near 
  and 
  along 
  the 
  

   foot 
  of 
  the 
  main 
  chaio, 
  but 
  they 
  are 
  irregular. 
  Streams 
  flow 
  in 
  most 
  

   every 
  direction, 
  and 
  the 
  mountains, 
  hills, 
  and 
  ridges 
  often 
  run 
  parallel 
  

   to 
  the 
  main 
  range. 
  In 
  this 
  case, 
  however, 
  it 
  appears 
  as 
  if 
  the 
  approach 
  

   to 
  the 
  main 
  chain 
  had 
  been 
  once 
  a 
  solid 
  huge 
  granite 
  plateau 
  about 
  

   3,000 
  feet 
  high, 
  " 
  with 
  only 
  such 
  unevenness 
  of 
  features 
  as 
  any 
  not 
  very 
  

   undulating 
  surface 
  would 
  produce.*' 
  Through 
  this 
  the 
  streams 
  originat- 
  

   ing 
  along 
  the 
  slopes 
  have 
  cut 
  a 
  remarkably 
  straight 
  easterly 
  course 
  to 
  

   the 
  plaiu. 
  Mr. 
  Archibald 
  E. 
  Marvin, 
  assistant 
  geologist 
  and 
  leader 
  of 
  

   the 
  party 
  in 
  1873, 
  to 
  which 
  I 
  was 
  attached 
  as 
  chief 
  topographer, 
  de- 
  

   scribed 
  the 
  eastern 
  slope 
  of 
  the 
  Front 
  Eange 
  in 
  that 
  region 
  with 
  par- 
  

   ticular 
  ability. 
  He 
  remarks 
  : 
  

  

  " 
  This 
  mountain 
  zone 
  can 
  in 
  no 
  wise 
  be 
  regarded 
  as 
  made 
  up 
  in 
  distinct 
  ranges 
  or 
  a 
  

   system 
  of 
  ridges, 
  but 
  as 
  a 
  unit 
  in 
  itself, 
  having 
  characteristics 
  which 
  hold 
  very 
  uni- 
  

   formly 
  over 
  nearly 
  all 
  parts. 
  From 
  beneath 
  the 
  precipitous 
  crest, 
  from 
  all 
  the 
  gorges 
  

   and 
  amphitheaters 
  at 
  its 
  base, 
  flow 
  inniimerable 
  streams 
  which, 
  after 
  emerging 
  from 
  

   these 
  upper 
  canons 
  into 
  the 
  smoother 
  highlands, 
  soon 
  collect 
  into 
  a 
  few 
  principal 
  

   water-courses. 
  Flowing 
  in 
  a 
  generally 
  eastern 
  course, 
  these 
  gradually 
  sink 
  their 
  chan- 
  

   nels 
  deeper 
  and 
  deeper 
  into 
  the 
  rocks, 
  the 
  different 
  main 
  streams 
  uniting 
  their 
  callous 
  

   here 
  and 
  there, 
  and 
  finally 
  issue 
  from 
  their 
  deep-cut 
  gorges 
  in 
  the 
  mountain 
  front 
  to 
  

   flow 
  out 
  into 
  the 
  plains 
  and 
  into 
  the 
  Platte." 
  

  

  Again 
  he 
  says 
  : 
  

  

  " 
  The 
  tendency 
  of 
  these 
  cross-cutting 
  streams 
  is 
  to 
  throw 
  this 
  eastern 
  mountain 
  area 
  

   into 
  east 
  and 
  west 
  ridges. 
  These 
  ridges 
  are 
  seldom 
  sharp, 
  but 
  massive, 
  and 
  rather 
  

   than 
  striking 
  one 
  as 
  a 
  system 
  of 
  ridges, 
  it 
  impresses 
  one 
  as 
  a 
  systeni 
  of 
  deep-cut 
  river 
  

   channels." 
  

  

  He 
  closes 
  his 
  remarks 
  about 
  this 
  region 
  in 
  saying 
  : 
  

  

  "The 
  majority 
  of 
  these 
  ridges 
  rise 
  somewhat 
  above 
  8,000 
  feet, 
  while 
  the 
  plains 
  along 
  

   the 
  eastern 
  base 
  of 
  the 
  mountains 
  average 
  not 
  far 
  from 
  5,600 
  or 
  6,000 
  feet. 
  A 
  few 
  

   points 
  along 
  the 
  face 
  of 
  the 
  mountains 
  rise 
  higher 
  than 
  the 
  country 
  immediately 
  in 
  their 
  

   rear, 
  such 
  as 
  Boulder 
  and 
  Golden 
  Peaks, 
  and 
  Bear 
  Peak, 
  which 
  stand 
  close 
  to 
  the 
  

   mountain 
  edge. 
  But 
  as 
  a 
  whole 
  the 
  mountain 
  zone 
  lying 
  between 
  the 
  main 
  divide 
  

   and 
  the 
  plains 
  certainly 
  impresses 
  one 
  as 
  being, 
  with 
  a 
  few 
  exceptions, 
  a 
  region 
  of 
  uni- 
  

   form 
  or 
  gently 
  undulating 
  general 
  elevation, 
  carved 
  by 
  the 
  powers 
  of 
  erosion, 
  perhaps 
  

   j)artly 
  glacial 
  but 
  mostly 
  by 
  streams, 
  into 
  a 
  mountain 
  area 
  of 
  which 
  portions 
  are 
  ex- 
  

   ceedingly 
  rugged." 
  

  

  Following 
  from 
  the 
  exit 
  of 
  Clear 
  Creek 
  the 
  foot-hills 
  for 
  five 
  miles 
  in 
  

   a 
  northward 
  direction, 
  we 
  arrive 
  at 
  the 
  mouth 
  of 
  

  

  EALSTON 
  CANON, 
  

  

  through 
  which 
  comes 
  forth 
  a 
  creek 
  of 
  a 
  third 
  order 
  of 
  the 
  eastern 
  slope 
  

   drainage, 
  for 
  its 
  sources 
  lie 
  only 
  10 
  miles 
  from 
  the 
  hogback 
  to 
  the 
  west, 
  

   while 
  its 
  tributaries 
  consist 
  of 
  small 
  rivulets 
  not 
  over 
  2 
  to 
  3 
  miles 
  in 
  

   length. 
  

  

  