﻿170 
  REPORT 
  UNITED 
  STATES 
  GEOLOGICAL 
  SURVEY. 
  

  

  the 
  mountains 
  rise 
  far 
  above 
  them, 
  showing 
  the 
  horizontal 
  edges 
  of 
  their 
  

   variegated 
  strata. 
  Between 
  the 
  two 
  nearest 
  forks 
  farther 
  west 
  station 
  

   37 
  is 
  located 
  on 
  an 
  isolated 
  outcrop 
  of 
  trachyte. 
  This 
  is 
  but 
  a 
  remnant 
  

   of 
  the 
  main 
  body, 
  separated 
  from 
  it 
  by 
  erosion. 
  Compact 
  trachyte 
  com- 
  

   poses 
  the 
  base 
  of 
  the 
  hill, 
  while 
  conglomerate 
  forms 
  its 
  summit. 
  Cre- 
  

   taceous 
  shales 
  surround 
  it 
  on 
  all 
  sides, 
  and 
  are 
  underlying 
  the 
  volcanic 
  

   rock. 
  Both 
  creeks 
  head 
  at 
  the 
  continental 
  divide 
  and 
  flow 
  through 
  nar- 
  

   row, 
  deep, 
  trachytic 
  caSons, 
  whence 
  they 
  emerge 
  and 
  enter 
  the 
  adjoining 
  

   Cretaceous 
  valley. 
  The 
  western 
  one 
  of 
  the 
  two, 
  Eio 
  Huerto, 
  flows 
  through 
  

   a 
  meadow, 
  after 
  leaving 
  its 
  caSon, 
  that 
  formerly 
  constituted 
  the 
  bed 
  of 
  

   a 
  glacial 
  lake. 
  (See 
  Appendix 
  A.) 
  Northwest 
  of 
  station 
  37 
  is 
  station 
  

   36, 
  located 
  at 
  an 
  altitude 
  of 
  11,347 
  feet 
  on 
  a 
  southward 
  spur 
  of 
  the 
  main 
  

   range. 
  Again 
  it 
  is 
  trachyte 
  that 
  forms 
  the 
  peak. 
  The 
  lower 
  strata 
  

   belonging 
  to 
  the 
  series 
  overlie 
  Cretaceous 
  beds, 
  and 
  are 
  followed 
  higher 
  

   up 
  by 
  the 
  conglomerate. 
  At 
  this 
  locality 
  the 
  latter 
  shows 
  a 
  light 
  grey 
  

   to 
  greyish-brown 
  color, 
  and 
  is 
  more 
  readily 
  disintegrated 
  than 
  near 
  

   Pagosa 
  Peak. 
  Near 
  its 
  upper 
  edge 
  a 
  stratum 
  of 
  porphyritic 
  pitch- 
  

   stone 
  was 
  found, 
  varying 
  in 
  thickness 
  from 
  6 
  to 
  18 
  inches. 
  A 
  portion 
  

   of 
  this 
  must 
  have 
  flowed 
  upon 
  the 
  conglomerate 
  while 
  the 
  latter 
  was 
  

   yet 
  under 
  water, 
  because 
  specimens 
  closely 
  resembling 
  pumice 
  are 
  found 
  

   with 
  it, 
  that 
  have 
  probably 
  assumed 
  their 
  present 
  texture 
  in 
  consequence 
  

   of 
  having 
  been 
  cooled 
  in 
  water. 
  On 
  this 
  peak 
  the 
  thickness 
  of 
  the 
  con- 
  

   glomerate 
  stratum 
  is 
  about 
  600 
  feet, 
  having 
  decreased 
  toward 
  the 
  north, 
  

   and 
  still 
  farther 
  in 
  the 
  same 
  direction 
  its 
  thickness 
  is 
  even 
  more 
  dimin- 
  

   ished. 
  Beds 
  of 
  trachyte 
  showing 
  a 
  variety 
  of 
  colors 
  overlie 
  it. 
  From 
  

   this 
  station 
  the 
  outcrop 
  of 
  the 
  trachytic 
  conglomerate 
  can 
  be 
  followed 
  

   for 
  a 
  considerable 
  distance 
  along 
  the 
  steep 
  edge 
  of 
  the 
  mountains. 
  It 
  

   appears, 
  generally 
  presenting 
  very 
  steep 
  or 
  precipitous 
  slopes, 
  all 
  around 
  

   the 
  edge, 
  and 
  in 
  the 
  canons 
  opening 
  into 
  the 
  valley. 
  In 
  this 
  entire 
  

   region 
  the 
  dip 
  of 
  the 
  trachytic 
  strata 
  remains 
  an 
  easterly 
  one, 
  varying 
  

   locally 
  on 
  account 
  of 
  subsidences 
  or 
  slides. 
  A 
  case 
  of 
  this 
  kind 
  occurs 
  

   near 
  the 
  mouth 
  of 
  the 
  canon 
  through 
  which 
  Eio 
  Huerto 
  east 
  of 
  station 
  

   36 
  flows. 
  There 
  the 
  conglomerate 
  was 
  soft, 
  within 
  reach 
  of 
  the 
  former 
  

   glacier 
  and 
  the 
  stream 
  afterward, 
  and 
  was 
  washed 
  away 
  in 
  part. 
  Thus 
  

   the 
  overlying 
  harder 
  strata 
  were 
  undermined 
  and 
  dropped 
  down 
  on 
  

   either 
  side 
  of 
  the 
  creek, 
  now 
  forming 
  a 
  steep 
  synclinal 
  fold, 
  broken 
  at 
  

   its 
  deepest 
  depression. 
  

  

  West 
  of 
  station 
  36 
  flows 
  Weeminuche 
  Creek, 
  heading 
  at 
  station 
  35. 
  

   This 
  latter 
  station 
  was 
  made 
  on 
  an 
  elevated 
  cone 
  in 
  the 
  plateau-like 
  

   summit 
  of 
  the 
  range, 
  is 
  situated 
  on 
  the 
  continental 
  divide, 
  and 
  reaches 
  

   an 
  altitude 
  of 
  12,889 
  feet. 
  Weeminuche 
  Creek 
  runs 
  but 
  a 
  short 
  distance 
  

   in 
  trachyte, 
  as 
  this 
  is 
  worn 
  away 
  farther 
  down, 
  exposing 
  first 
  the 
  met- 
  

   amorphic 
  granite, 
  and 
  then 
  the 
  underlying 
  Cretaceous 
  beds. 
  This 
  gran- 
  

   ite 
  is 
  a 
  continuation 
  of 
  the 
  main 
  metamorphic 
  area 
  of 
  the 
  Quartzit© 
  

   Mountains 
  farther 
  west, 
  and 
  closely 
  resembles 
  that 
  described 
  from 
  station 
  

   52 
  of 
  1874*. 
  It 
  extends 
  northward 
  for 
  some 
  distance 
  toward 
  Weeminuche 
  

   Pass, 
  and 
  the 
  well-worn 
  Ute 
  trail 
  leads 
  over 
  it 
  from 
  there. 
  West 
  of 
  it, 
  

   the 
  small 
  plateau 
  at 
  which 
  the 
  west 
  fork 
  of 
  Weeminuche 
  Creek 
  heads, 
  

   is 
  covered 
  with 
  trachyte. 
  On 
  the 
  eastern 
  side 
  of 
  Weeminuche 
  Pass 
  the 
  

   spurs 
  of 
  the 
  range 
  are 
  analogous 
  in 
  the 
  arrangement 
  of 
  their 
  trachytic 
  

   strata 
  to 
  those 
  of 
  most 
  of 
  the 
  Rio 
  Grande 
  Pyramid 
  group. 
  The 
  con- 
  

   glomerate 
  has 
  thinned 
  out 
  considerably, 
  and 
  is 
  no 
  longer 
  a 
  prominent 
  

   feature 
  of 
  the 
  blufis, 
  though 
  still 
  found, 
  and 
  the 
  trachytic 
  beds 
  have 
  

   changed 
  slightly, 
  so 
  as 
  to 
  fully 
  agree 
  with 
  the 
  characteristics 
  given 
  for 
  

   No. 
  3, 
  farther 
  west. 
  Above 
  the 
  conglomerate 
  occur 
  the 
  variegated 
  

  

  * 
  Report 
  United 
  States 
  Geological 
  Survey, 
  1874, 
  page 
  189. 
  

  

  