﻿42 
  REPORT 
  UNITED 
  STATES 
  GEOLOGICAL 
  SURVEY. 
  

  

  below 
  the 
  head 
  of 
  the 
  cauon. 
  The 
  rocks 
  are 
  mainly 
  Dakota-sandstones, 
  

   dipping 
  about 
  5° 
  to 
  the 
  northeast. 
  

  

  Just 
  below 
  the 
  mouth 
  of 
  the 
  Eio 
  de 
  las 
  Vacas 
  there 
  is 
  a 
  bed 
  of 
  trachyte. 
  

   On 
  the 
  eastern 
  side 
  the 
  river 
  has 
  cut 
  into 
  this 
  rock, 
  which 
  rises 
  in 
  bluffs 
  

   about 
  150 
  feet 
  above 
  the 
  river. 
  These 
  bluffs 
  are 
  very 
  regular. 
  On 
  the 
  

   western 
  side 
  the 
  mass 
  of 
  trachyte 
  does 
  not 
  seem 
  to 
  be 
  interlaminated, 
  

   but 
  intruded 
  irregularly, 
  sometimes 
  showing 
  at 
  the 
  top 
  of 
  the 
  caiion. 
  

   The 
  band 
  of 
  lignite 
  usually 
  found 
  in 
  the 
  Dakota 
  sandstones 
  is 
  here 
  

   changed 
  to 
  anthracite, 
  probably 
  from 
  the 
  effect 
  of 
  heat 
  during 
  the 
  intru- 
  

   sion 
  of 
  this 
  igneous 
  rock. 
  At 
  station 
  11 
  the 
  cauon 
  is 
  about 
  500 
  feet 
  deep, 
  

   and 
  at 
  station 
  10 
  very 
  little 
  lower. 
  A 
  mile 
  back 
  of 
  station 
  11 
  there 
  are 
  

   some 
  higher 
  points, 
  which 
  mark 
  in 
  all 
  probability 
  the 
  presence 
  of 
  rem- 
  

   nants 
  of 
  higher 
  beds 
  with 
  trachytic 
  intrusions. 
  (See 
  Fig. 
  4, 
  Plate 
  III.) 
  

   East 
  of 
  station 
  15 
  there 
  is 
  a 
  depression, 
  in 
  which 
  the 
  creek, 
  flowing 
  into 
  

   the 
  Uncompahgre 
  above 
  station 
  11, 
  rises. 
  The 
  dip 
  of 
  th^ 
  rock 
  at 
  station 
  

   10 
  is 
  more 
  to 
  the 
  eastward 
  than 
  it 
  is 
  at 
  the 
  head 
  of 
  the 
  canon, 
  where 
  there 
  

   is 
  an 
  inclination 
  northward. 
  

  

  The 
  east 
  side 
  of 
  the 
  Uncompahgre, 
  from 
  the 
  mouth 
  of 
  the 
  caiion 
  to 
  Ce- 
  

   dar 
  Creek, 
  rises 
  to 
  the 
  hills 
  about 
  station 
  6. 
  The 
  strata 
  are 
  of 
  Middle 
  

   and 
  U 
  pper 
  Cretaceous 
  age, 
  and 
  the 
  soil 
  derived 
  from 
  their 
  erosion 
  is 
  alka- 
  

   line, 
  almost 
  destitute 
  of 
  vegetation, 
  sage-brush 
  and 
  grease-wood 
  ex- 
  

   cepted. 
  Near 
  the 
  river 
  terraces 
  occur. 
  These, 
  however, 
  are 
  more 
  marked 
  

   on 
  the 
  western 
  side, 
  farther 
  north, 
  where 
  they 
  extend 
  to 
  the 
  Gunnison. 
  

   The 
  dip 
  of 
  the 
  rocks 
  underlying 
  is 
  to 
  the 
  east. 
  Kear 
  the 
  river 
  there 
  

   are 
  Middle 
  Cretaceoiis 
  beds, 
  which 
  gradually 
  disappear 
  as 
  we 
  go 
  west- 
  

   ward 
  toward 
  the 
  crest 
  which 
  marks 
  the 
  western 
  edge 
  of 
  this 
  sloping 
  

   Uncompahgre 
  plateau. 
  The 
  crest 
  is 
  from 
  8,500 
  to 
  10,000 
  feet 
  high. 
  Its 
  

   direction 
  is 
  more 
  west 
  of 
  north 
  than 
  is 
  the 
  course 
  of 
  the 
  Uncompahgre, 
  

   (See 
  Fig. 
  3, 
  Plate 
  II.) 
  The 
  Gunnison, 
  below 
  the 
  mouth 
  of 
  the 
  Uncom- 
  

   pahgre, 
  however, 
  gradually 
  takes 
  a 
  course 
  which 
  is 
  in 
  line 
  with 
  the 
  

   course 
  of 
  the 
  upper 
  part 
  of 
  the 
  Uncompahgre, 
  so 
  that 
  the 
  widest 
  part 
  

   of 
  the 
  plateau 
  is 
  opposite 
  the 
  angle 
  included 
  between 
  the 
  Gunnison 
  and 
  

   Uncompahgre 
  Elvers. 
  The 
  width 
  here 
  is 
  about 
  30 
  miles. 
  

  

  From 
  a 
  point 
  five 
  miles 
  up 
  the 
  Uncompahgre 
  from 
  its 
  mouth, 
  to 
  

   station 
  23, 
  is 
  a 
  distance 
  of 
  27^ 
  miles. 
  Station 
  23 
  has 
  an 
  elevation 
  of 
  

   9,228 
  feet, 
  which 
  is 
  3,872 
  feet 
  above 
  the 
  Uncompahgre 
  at 
  the 
  point 
  just 
  

   mentioned. 
  This 
  is 
  an 
  average 
  rise 
  of 
  a 
  little 
  over 
  140 
  feet 
  per 
  mile. 
  

   For 
  10 
  or 
  12 
  miles 
  from 
  the 
  Uncompahgre, 
  however, 
  the 
  surface 
  is 
  very 
  

   nearly 
  uniform, 
  and 
  then 
  we 
  have 
  a 
  comparatively 
  gentle 
  monoclinal 
  

   fold, 
  which 
  gradually 
  becomes 
  a 
  plateau-top 
  as 
  we 
  approach 
  station 
  23. 
  

   The 
  level 
  portion 
  near 
  the 
  Uncompahgre 
  is 
  beautifully 
  terraced, 
  and 
  com- 
  

   posed 
  of 
  cretaceous 
  shales 
  underlaid 
  with 
  sandstones 
  of 
  the 
  Dakota 
  

   group. 
  The 
  shales 
  gradually 
  disappear 
  as 
  we 
  recede 
  from 
  the 
  river. 
  

   (See 
  sections 
  in 
  Plate 
  III.) 
  

  

  From 
  station 
  18 
  to 
  camp 
  l^o, 
  20, 
  on 
  the 
  Uncompahgre, 
  is 
  a 
  distance 
  of 
  

   18 
  miles. 
  The 
  elevation 
  of 
  station 
  IS 
  is 
  9,557 
  feet, 
  3,745 
  above 
  the 
  level 
  

   of 
  the 
  Uncompahgre, 
  where 
  the 
  wagon-road 
  crosses 
  it, 
  (near 
  camp 
  20.) 
  

   Here 
  the 
  rise 
  toward 
  the 
  crest 
  begins 
  much 
  sooner. 
  There 
  are 
  three 
  

   branches 
  of 
  the 
  Uncompahgre 
  flowing 
  across 
  this 
  slope 
  toward 
  the 
  

   northeast. 
  During 
  the 
  summer 
  they 
  are 
  dry, 
  and 
  their 
  direction 
  is 
  

   marked 
  only 
  by 
  the 
  canons 
  they 
  have 
  cut 
  in 
  the 
  sandstone. 
  They 
  

   have 
  but 
  few 
  lateral 
  canons. 
  Kising 
  near 
  the 
  crest, 
  they 
  keep 
  (with 
  

   the 
  exception 
  of 
  tbe 
  southern) 
  a 
  nearly 
  uniform 
  course 
  to 
  within 
  

   about 
  7 
  miles 
  of 
  the 
  Uncompahgre, 
  when 
  they 
  turn 
  abruptly 
  to- 
  

   ward 
  the 
  north, 
  flowing 
  more 
  nearly 
  parallel 
  with 
  the 
  Uncompahgre, 
  

   until 
  finally 
  they 
  flow 
  iiito 
  it. 
  Is^'ear 
  the 
  sources 
  of 
  these 
  creeks 
  the 
  

  

  