﻿'66 
  EEPORT 
  UNITED 
  STATES 
  GEOLOGICAL 
  SURVEY. 
  

  

  tweea 
  the 
  Gunnison 
  and 
  San 
  Migael 
  and 
  Dolores 
  Elvers, 
  commencing 
  

   on 
  the 
  eastern 
  side, 
  and 
  following 
  it 
  around 
  south 
  of 
  the 
  Grand 
  toward 
  

   the 
  Dolores. 
  

  

  The 
  Gunnison 
  Eiver, 
  from 
  its 
  Grand 
  Canon 
  to 
  the 
  mouth, 
  is 
  in 
  sedi- 
  

   mentary 
  rocks. 
  Going 
  west 
  from 
  the 
  lower 
  canon 
  and 
  ascending 
  to 
  the 
  

   plateau, 
  we 
  find 
  on 
  one 
  of 
  the 
  branches 
  of 
  Unaweep 
  Canon, 
  a 
  strip 
  of 
  

   gneissic 
  rock. 
  I 
  leave 
  the 
  consideration 
  of 
  the 
  Unaweep 
  CaQon 
  gneissic 
  

   rocks 
  for 
  the 
  present, 
  and 
  go 
  north. 
  Here 
  we 
  find 
  on 
  nearly 
  all 
  the 
  

   streams 
  flowing 
  to 
  the 
  Gunnison, 
  narrow 
  belts 
  of 
  Archaean 
  rocks. 
  A 
  lit- 
  

   tle 
  farther 
  north, 
  on 
  high 
  bluffs 
  southwest 
  of 
  the 
  mouth 
  of 
  the 
  Gunnison, 
  

   we 
  find 
  these 
  narrow 
  belts 
  connected 
  with 
  a 
  line 
  extending 
  along 
  the 
  

   edge 
  of 
  the 
  bluffs, 
  and 
  marking 
  a 
  point 
  where, 
  instead 
  of 
  the 
  monocli- 
  

   nal 
  fold, 
  usual 
  along 
  this 
  side 
  of 
  the 
  plateau, 
  we 
  have 
  a 
  fault. 
  On 
  the 
  west 
  

   side 
  resting 
  on 
  the 
  granitic 
  or 
  gneissic 
  rocks, 
  are 
  red 
  sandstones 
  (Trias- 
  

   sic"?) 
  with 
  a 
  gentle 
  inclination 
  eastward. 
  On 
  the 
  eastern 
  side, 
  the 
  sand- 
  

   stones 
  of 
  the 
  Dakota 
  group 
  (Cretaceous 
  ISTo. 
  1) 
  rest 
  on 
  the 
  gneissic 
  

   rocks, 
  dipping 
  to 
  the 
  eastward 
  also, 
  but 
  with 
  a 
  much 
  greater 
  inclination, 
  

   sometimes 
  being 
  almost 
  vertical. 
  The 
  dip, 
  however, 
  as 
  we 
  go 
  toward 
  

   the 
  rivers, 
  decreases, 
  the 
  ends 
  of 
  the 
  strata 
  simply 
  being 
  turned 
  up 
  

   steeply 
  near 
  the 
  granite. 
  This 
  belt 
  is 
  not 
  extensive, 
  the 
  fold 
  soon 
  com- 
  

   ing 
  in 
  again 
  and 
  covering 
  it. 
  I 
  was 
  unable 
  to 
  get 
  down 
  to 
  the 
  rocks 
  

   here, 
  but 
  they 
  seemed 
  to 
  be 
  mainly 
  dark 
  micaceous 
  schists. 
  From 
  our 
  

   point 
  of 
  view, 
  no 
  evidences 
  of 
  stratification 
  were 
  observed, 
  though 
  the 
  

   dip 
  is 
  probably 
  to 
  the 
  northeast, 
  as 
  was 
  observed 
  farther 
  west. 
  

  

  Ou 
  the 
  creeks 
  rising 
  north 
  of 
  stations 
  47, 
  46, 
  and 
  45, 
  and 
  flowing 
  into 
  

   Grand 
  River, 
  we 
  have 
  some 
  narrow 
  strips 
  of 
  gneissic 
  rocks. 
  On 
  the 
  most 
  

   northern 
  of 
  these, 
  the 
  principal 
  stream, 
  (Little 
  Dolores,) 
  we 
  have 
  mica 
  

   schists 
  and 
  quartzites 
  dipping 
  northeast 
  at 
  an 
  angle 
  of 
  GO"^ 
  to 
  70°. 
  They 
  

   are 
  generally 
  dark-colored, 
  with 
  seamsof 
  quartz 
  and 
  feldspar, 
  and 
  appear 
  

   only 
  at 
  the 
  bottom 
  of 
  the 
  caiion. 
  On 
  them 
  the 
  red 
  beds 
  rest, 
  dippingto 
  the 
  

   north, 
  or 
  perhaps 
  a 
  few 
  degrees 
  east 
  of 
  north, 
  the 
  inclination 
  being 
  from 
  

   3° 
  to 
  5C'. 
  On 
  the 
  north 
  side 
  of 
  the 
  main 
  stream 
  the 
  angle 
  increases, 
  throw- 
  

   ing 
  the 
  red 
  beds 
  to 
  the 
  bottom 
  of 
  the 
  caiion, 
  and 
  the 
  granitic 
  rock, 
  there- 
  

   fore, 
  does 
  not 
  show 
  on 
  that 
  side. 
  Grand 
  Eiver 
  appears 
  to 
  be 
  entirely 
  

   in 
  the 
  red 
  beds. 
  Following 
  the 
  plateau 
  around 
  to 
  the 
  west 
  side 
  at 
  sta- 
  

   tion 
  47 
  we 
  find 
  ourselves 
  again 
  on 
  the 
  edge 
  of 
  an 
  Archaean 
  area, 
  which 
  

   commences 
  south 
  of 
  stations 
  46 
  and 
  47 
  and 
  extends 
  toward 
  the 
  north- 
  

   west 
  in 
  a 
  narrow 
  belt 
  as 
  far 
  as 
  we 
  could 
  see, 
  marking 
  a 
  line 
  of 
  faulting. 
  

   Here 
  the 
  red 
  beds 
  again 
  show 
  themselves 
  resting 
  directly 
  on 
  these 
  older 
  

   rocks. 
  Going 
  east 
  of 
  south 
  from 
  station 
  47 
  we 
  come 
  to 
  Unaweep 
  

   Canon, 
  in 
  which 
  the 
  greater 
  part 
  of 
  the 
  walls 
  are 
  granitic. 
  Commenc- 
  

   ing 
  at 
  the 
  eastern 
  end 
  of 
  the 
  caiion, 
  we 
  find 
  at 
  first 
  that 
  the 
  walls 
  are 
  

   simply 
  of 
  stratified 
  rocks. 
  Station 
  54 
  is 
  on 
  the 
  Dakota 
  sandstones, 
  

   which 
  dip 
  approximately 
  eastward. 
  The 
  bed 
  of 
  the 
  creek 
  is 
  679 
  feet 
  

   below 
  the 
  station. 
  Here 
  we 
  first 
  meet 
  with 
  the 
  granite 
  as 
  a 
  narrow 
  strip 
  

   bordering 
  the 
  creek. 
  As 
  we 
  go 
  up 
  the 
  caiion 
  the 
  granite 
  walls 
  soon 
  

   appear 
  and 
  gradually 
  rise 
  higher 
  and 
  higher. 
  At 
  first 
  the 
  walls 
  were 
  

   red 
  sandstones, 
  but 
  as 
  they 
  have 
  a 
  dip 
  of 
  4° 
  to 
  5^ 
  and 
  the 
  stream-bed 
  

   only 
  an 
  inclination 
  of 
  about 
  2"^ 
  with 
  the 
  horizon, 
  they 
  soon 
  form 
  simply 
  

   a 
  capping 
  on 
  top 
  of 
  the 
  granite 
  wall. 
  At 
  station 
  40 
  the 
  granite 
  wall 
  is 
  

   about 
  173 
  feet 
  high. 
  At 
  station 
  38, 
  a 
  distance 
  of 
  nearly 
  six 
  miles 
  in 
  an 
  

   air-line 
  west 
  from 
  station 
  40, 
  the 
  top 
  of 
  the 
  granite 
  is 
  815 
  above 
  the 
  creek- 
  

   bed. 
  Camp 
  31 
  was 
  on 
  the 
  top 
  of 
  the 
  granite, 
  near 
  the 
  edge 
  of 
  the 
  caiion 
  

   close 
  to 
  this 
  station. 
  Here 
  the 
  rock 
  was 
  a 
  bluish-gray 
  porphy 
  ritic 
  granite, 
  

   with 
  numerous 
  feldspathic 
  crystals. 
  There 
  was 
  no 
  trace 
  of 
  stratification, 
  

   although 
  in 
  a 
  number 
  of 
  places 
  I 
  noticed 
  in 
  the 
  rock, 
  spots 
  that 
  had 
  a 
  

  

  