﻿52 
  EEPORT 
  UNITED 
  STATES 
  GEOLOGICAL 
  SURVEY. 
  

  

  the 
  principal 
  drainage 
  is 
  from 
  Lone 
  Cone 
  and 
  the 
  San 
  Miguel 
  Mount- 
  

   ains. 
  These 
  creeks 
  flow 
  almost 
  due 
  north, 
  rising 
  in 
  the 
  Middle 
  Creta- 
  

   ceous 
  shales, 
  but 
  soon 
  cutting 
  through 
  them, 
  and 
  finally 
  joining 
  the 
  

   river 
  in 
  the 
  Jurassic 
  or 
  Upper 
  Triassic? 
  strata. 
  

  

  The 
  plateau 
  on 
  the 
  northeast 
  side 
  of 
  the 
  river 
  is 
  comparatively 
  level 
  

   and 
  covered 
  with 
  groves 
  of 
  pines. 
  The 
  surface 
  rock 
  is 
  the 
  Dakota 
  

   sandstone. 
  All 
  the 
  creeks 
  cut 
  canons 
  through 
  it 
  on 
  their 
  way 
  to 
  the 
  

   river, 
  and 
  the 
  plateau 
  is 
  cut 
  into 
  mesas, 
  especially 
  noticeable 
  near 
  the 
  

   San 
  Miguel. 
  Between 
  station 
  20 
  and 
  the 
  crest 
  of 
  the 
  Uncompahgre 
  

   plateau 
  there 
  is 
  a 
  broad 
  anticlinal 
  fold, 
  so 
  slight 
  that 
  in 
  looking 
  tlown 
  

   upon 
  it 
  from 
  the 
  Uncompahgre 
  plateau 
  it 
  is 
  not 
  noticed. 
  

  

  The 
  first 
  creek 
  joining 
  the 
  San 
  Miguel 
  from 
  the 
  northeast 
  after 
  it 
  

   fairly 
  emerges 
  from 
  the 
  mountains 
  has 
  been 
  named 
  " 
  Del 
  Codo," 
  on 
  ac- 
  

   count 
  of 
  the 
  curious 
  elbow 
  in 
  its 
  course. 
  Eising 
  in 
  the 
  group 
  of 
  vol- 
  

   canic 
  peaks 
  forming 
  the 
  western 
  part 
  of 
  the 
  Uncompahgre 
  Mountains, 
  

   it 
  flows 
  nortliward 
  across 
  the 
  Middle 
  Cretaceous 
  shales, 
  approximately 
  

   parallel 
  to 
  the 
  branches 
  of 
  the 
  Uncompahgre, 
  which 
  rise 
  in 
  the 
  northern 
  

   face 
  of 
  the 
  Uncompahgre 
  Mountains. 
  From 
  them 
  it 
  is 
  separated 
  by 
  a 
  

   spur-like 
  ridge 
  capped 
  with 
  Middle 
  Cretaceous. 
  The 
  creek 
  soon 
  cuts 
  

   into 
  the 
  Dakota 
  sandstones, 
  and 
  seven 
  miles 
  from 
  its 
  head 
  deviates 
  from 
  

   its 
  northward 
  course 
  and 
  flows 
  northwest 
  for 
  about 
  three 
  miles, 
  when 
  

   it 
  makes 
  a 
  sharp 
  turn 
  or 
  elbow 
  and 
  flows 
  a 
  little 
  west 
  of 
  south 
  in 
  

   deep 
  caiion 
  to 
  the 
  San 
  Miguel, 
  joining 
  the 
  river 
  in 
  the 
  red 
  sandstones 
  

   of 
  the 
  Trias 
  1 
  In 
  this 
  latter 
  course 
  it 
  is 
  joined 
  by 
  three 
  short 
  streams 
  

   in 
  caiion, 
  that 
  rise 
  in 
  the 
  same 
  grouj) 
  of 
  mountains 
  with 
  the 
  main 
  

   stream. 
  In 
  these 
  canons, 
  as 
  in 
  all 
  those 
  cut 
  in 
  the 
  plateau, 
  there 
  is 
  a 
  belt 
  

   of 
  the 
  Lower 
  Dakota 
  group 
  and 
  of 
  the 
  Jurassic 
  shales 
  bordering 
  the 
  

   stream.s. 
  

  

  The 
  western 
  crest 
  of 
  the 
  Uncompahgre 
  Plateau 
  begins 
  on 
  the 
  spur 
  

   separating 
  the 
  Eio 
  del 
  Codo 
  from 
  the 
  Dallas 
  Fork 
  of 
  the 
  Uncompahgre. 
  

   It 
  is 
  from 
  seven 
  to 
  ten 
  miles 
  from 
  the 
  San 
  Miguel, 
  and 
  is 
  about 
  2,000 
  

   feet 
  above 
  the 
  general 
  level 
  of 
  the 
  San 
  Miguel 
  plateau. 
  From 
  station 
  18 
  

   to 
  station 
  26, 
  a 
  distance 
  of 
  30 
  miles, 
  the 
  direction 
  of 
  the 
  crest 
  is 
  north 
  

   60° 
  west. 
  The 
  drainage 
  as 
  far 
  as 
  station 
  21 
  is 
  by 
  creeks 
  that 
  cut 
  across 
  

   the 
  crest 
  at 
  right 
  angles 
  to 
  its 
  direction. 
  These 
  creeks 
  all 
  unite 
  in 
  one 
  

   stream, 
  Muache 
  Creek, 
  which 
  joins 
  the 
  San 
  Miguel 
  before 
  it 
  bends 
  to 
  the 
  

   westward. 
  The 
  gashes 
  in 
  the 
  crest 
  afford 
  an 
  excellent 
  opportunity 
  to 
  

   study 
  its 
  structure. 
  The 
  primary 
  condition 
  is 
  a 
  monoclinal 
  fold, 
  the 
  

   sandstones 
  of 
  the 
  Upper 
  Dakota 
  group 
  being 
  in 
  general 
  the 
  surface 
  

   formation. 
  At 
  station 
  15 
  the 
  fold 
  is 
  very 
  slight, 
  aud 
  although 
  the 
  strata 
  

   are 
  to 
  a 
  great 
  extent 
  concealed, 
  there 
  is 
  but 
  little 
  doubt 
  that 
  shales 
  of 
  

   Middle 
  Cretaceous 
  age 
  underlie 
  the 
  drift 
  scattered 
  on 
  the 
  hills. 
  Station 
  

   15 
  may 
  have 
  a 
  capping 
  of 
  breccia, 
  although 
  the 
  beds 
  are 
  concealed. 
  As 
  

   we 
  go 
  northwest 
  from 
  station 
  15, 
  which 
  has 
  a 
  capping 
  of 
  shales, 
  the 
  fold 
  

   becomes 
  more 
  marked, 
  the 
  shales 
  disappear, 
  and 
  the 
  Dakota 
  sandstone 
  

   is 
  folded 
  over 
  the 
  crest, 
  its 
  continuity 
  being 
  unbroken. 
  (Section, 
  Fig. 
  3 
  

   Plate 
  III.) 
  From 
  the 
  crest 
  it 
  slopes 
  gently 
  to 
  the 
  Uncompahgre 
  River. 
  

   In 
  the 
  third 
  creek, 
  northwest 
  from 
  station 
  15, 
  the 
  fold 
  has 
  become 
  

   greater, 
  (Fig. 
  2, 
  Plate 
  III,) 
  and 
  in 
  the 
  caiion 
  cut 
  by 
  the 
  stream 
  there 
  is 
  

   the 
  following 
  section 
  : 
  

  

  1. 
  Upper 
  Dakota, 
  sandstone. 
  

  

  2. 
  Lower 
  Dakota, 
  shales. 
  

  

  '3. 
  Jurassic 
  variegated 
  beds. 
  

  

  4. 
  Massive 
  red 
  sandstone, 
  light 
  colored. 
  

  

  Five 
  or 
  six 
  miles 
  farther 
  northwest 
  is 
  another 
  creek 
  which 
  cuts 
  deeper 
  

  

  