﻿46 
  GEOLOGICAL 
  SURVEY 
  OF 
  THE 
  TERRITORIES. 
  

  

  surface, 
  sloping 
  in 
  a 
  gradual 
  and 
  gentle 
  curve 
  toward 
  the 
  river, 
  gashed 
  

   by 
  the 
  outcoming 
  streams 
  Sowing 
  at 
  right 
  angles 
  to 
  the 
  axis 
  of 
  the 
  fold. 
  

   This 
  necessarily 
  leaves 
  between 
  the 
  creeks 
  broad 
  masses 
  of 
  rock 
  with 
  

   square-cut 
  edges, 
  curved 
  only 
  in 
  one 
  direction, 
  viz, 
  from 
  the 
  top 
  of 
  the 
  

   fold 
  to 
  the 
  river. 
  

  

  The 
  creek 
  just 
  described 
  carries 
  water 
  at 
  the 
  heads 
  of 
  both 
  branches, 
  

   but 
  it 
  disappears 
  before 
  the 
  Gunnison 
  is 
  reached. 
  Proceeding 
  north, 
  

   we 
  find 
  three 
  more 
  tributaries 
  of 
  the 
  Gunnison. 
  The 
  first 
  is 
  a 
  small 
  

   creek, 
  heading 
  only 
  five 
  miles 
  from 
  the 
  river. 
  The 
  next 
  is 
  longer, 
  and 
  

   spreads 
  into 
  three 
  branches, 
  all 
  of 
  which 
  cut 
  profound 
  chasms, 
  which, 
  

   when 
  we 
  saw 
  them 
  in 
  the 
  latter 
  i)art 
  of 
  July, 
  were 
  perfectly 
  dry. 
  We 
  

   found 
  it 
  impossible 
  to 
  get 
  down 
  into 
  these 
  caiions. 
  Commencing 
  at 
  the 
  

   heads 
  of 
  the 
  creeks 
  and 
  following 
  them 
  for 
  a 
  short 
  distance, 
  we 
  find 
  them 
  

   plunging 
  abruptly 
  over 
  precipitous 
  edges 
  to 
  a 
  level 
  from 
  100 
  to 
  200 
  feet 
  

   lower, 
  and 
  then 
  descending 
  through 
  rapidly 
  deepening 
  caiions, 
  from 
  which 
  

   they 
  flow 
  abruptly 
  into 
  a 
  comparatively 
  open 
  country 
  to 
  the 
  Gunnison. 
  

   Following 
  the 
  edges 
  of 
  these 
  canons, 
  we 
  come 
  to 
  the 
  edge 
  of 
  precipices 
  

   800 
  to 
  1,000 
  feet 
  high, 
  overlooking 
  the 
  valley 
  in 
  which 
  the 
  Gunnison 
  and 
  

   Grand 
  Rivers 
  unite. 
  These 
  tongue-like 
  points 
  are 
  of 
  the 
  bare 
  light-col- 
  

   ored 
  sandstone 
  which 
  marks 
  the 
  top 
  of 
  the 
  red 
  beds. 
  In 
  the 
  caiions 
  and 
  

   along 
  the 
  front 
  of 
  the 
  bluft-like 
  prominence 
  we 
  could 
  see 
  granite-rocks 
  

   below 
  the 
  red 
  beds, 
  and 
  beyond, 
  at 
  a 
  much 
  lower 
  level, 
  were 
  the 
  up- 
  

   turned 
  edges 
  of 
  the 
  Dakota 
  sandstones. 
  Instead 
  of 
  the 
  uninterrupted 
  

   monoclinal 
  fold, 
  we 
  have 
  here 
  a 
  fault, 
  with 
  the 
  ends 
  of 
  the 
  beds 
  on 
  the 
  

   downthrow 
  dragged 
  up. 
  It 
  is 
  impossible 
  to 
  tell 
  the 
  amount 
  of 
  the 
  fault, 
  

   for 
  we 
  were 
  unable 
  to 
  get 
  down 
  to 
  the 
  edges 
  of 
  the 
  Dakota 
  sandstones, 
  

   but 
  they 
  must 
  have 
  been 
  at 
  least 
  800 
  feet 
  below 
  us. 
  The 
  fault 
  continues 
  

   some 
  distance 
  to 
  the 
  north, 
  where 
  we 
  could 
  see 
  the 
  Dakota 
  sandstones 
  

   standing 
  in 
  vertical 
  position 
  ; 
  and 
  still 
  further 
  beyond 
  the 
  fold 
  again 
  

   showed, 
  the 
  continuity 
  of 
  the 
  red 
  beds 
  being 
  unbroken, 
  the 
  outcrop 
  of 
  

   both 
  the 
  Jurassic 
  shales 
  and 
  the 
  Dakota 
  group 
  ending 
  before 
  the 
  sum- 
  

   mit 
  of 
  the 
  fold 
  is 
  reached. 
  This 
  fault 
  a 
  short 
  distance 
  farther 
  north 
  is 
  

   shown 
  in 
  Plate 
  II, 
  Fig. 
  1, 
  which 
  represents 
  a 
  section 
  across 
  the 
  plateau. 
  

   In 
  speaking 
  of 
  the 
  monoclinal 
  fold 
  in 
  the 
  report 
  for 
  1874, 
  I 
  referred 
  to 
  

   the 
  probability 
  of 
  its 
  degenerating 
  into 
  a 
  fault 
  as 
  we 
  followed 
  it 
  toward 
  

   the 
  north. 
  

  

  The 
  last 
  branch 
  of 
  the 
  Gunnison 
  from 
  the 
  west 
  joins 
  it 
  about 
  a 
  mile 
  

   and 
  a 
  half 
  above 
  its 
  mouth. 
  It 
  drains 
  the 
  country 
  south 
  of 
  station 
  52, 
  

   rising 
  in 
  the 
  upper 
  part 
  of 
  the 
  red 
  beds. 
  Here 
  it 
  flows 
  toward 
  the 
  

   north 
  for 
  six 
  miles 
  along 
  the 
  western 
  edge 
  of 
  a 
  mass 
  of 
  Jurassic 
  shales, 
  

   which 
  rest 
  on 
  the 
  red 
  beds, 
  and 
  are 
  capped 
  with 
  Dakota 
  sandstones. 
  

   The 
  strataAiere 
  dip 
  to 
  the 
  northeast. 
  After 
  flowing 
  to 
  the 
  northeast 
  for 
  

   six 
  miles 
  the 
  creek 
  turns 
  abruptly 
  to 
  the 
  northeast, 
  cutting 
  at 
  first 
  

   through 
  the 
  shales. 
  It 
  soon 
  reaches 
  the 
  massive 
  red 
  sandstones, 
  

   through 
  which 
  it 
  cuts 
  a 
  profound 
  caiion 
  to 
  the 
  gneiss, 
  and 
  cutting 
  across 
  

   the 
  fault 
  comes 
  out 
  into 
  the 
  Dakota 
  sandstones 
  in 
  the 
  valley 
  of 
  the 
  

   Grand 
  and 
  Gunnison 
  Rivers. 
  This 
  stream 
  repeats 
  the 
  history 
  of 
  nearly 
  

   all 
  the 
  creeks 
  in 
  this 
  region 
  in 
  being 
  dry. 
  The 
  hills 
  are 
  covered 
  with 
  a 
  

   growth 
  of 
  piiion 
  pines. 
  

  

  GRAND 
  RIVER. 
  

  

  Below 
  the 
  mouth 
  of 
  the 
  Gunnison, 
  Grand 
  River 
  at 
  first 
  flows 
  in 
  open 
  

   valley, 
  from 
  which 
  it 
  gradually 
  cuts 
  a 
  caiion 
  at 
  first 
  in 
  the 
  Cretaceous 
  

   strata 
  and 
  then 
  in 
  Jurassic 
  and 
  Triassic. 
  Its 
  course 
  is 
  a 
  few 
  degrees 
  

   north 
  of 
  west. 
  This 
  it 
  keeps 
  for 
  a 
  distance 
  of 
  about 
  twenty-six 
  miles 
  in 
  

  

  