﻿ENDLicH.] 
  SAWATCH 
  EANGE 
  EASTERN 
  SLOPE. 
  161 
  

  

  may 
  serve 
  as 
  a 
  guide 
  to 
  prospectors 
  and 
  miners. 
  Its 
  colors 
  vary 
  here, 
  as 
  

   farther 
  west. 
  Starting 
  from 
  white 
  they 
  pass 
  through 
  yellow 
  and 
  orange 
  

   to 
  a 
  brilliant 
  red, 
  deepening 
  at 
  places 
  into 
  a 
  dark 
  brown 
  and 
  maroon. 
  

   It 
  is 
  not 
  in 
  this 
  stratum 
  that 
  always 
  the 
  paying 
  lodes 
  are 
  found, 
  but 
  it 
  

   is 
  evidently 
  in 
  intimate 
  connection 
  with 
  the 
  lode-bearing 
  formations. 
  

   West 
  of 
  the 
  headwaters 
  of 
  the 
  San 
  Francisco, 
  stations 
  15 
  and 
  16 
  are 
  

   located, 
  at 
  elevations 
  of 
  12,515 
  feet 
  and 
  13,17(5 
  feet. 
  The 
  latter 
  is 
  a 
  high, 
  

   rounded 
  hill 
  covered 
  with 
  short 
  grass. 
  Over 
  it 
  leads 
  the 
  wagon-road 
  to 
  

   the 
  Summit 
  district. 
  Both 
  are 
  trachytic. 
  On 
  station 
  15 
  the 
  trachyte 
  

   weathers 
  in 
  thin 
  slabs. 
  It 
  is 
  of 
  a 
  brown 
  color, 
  containing 
  sanidite, 
  horn- 
  

   blende, 
  biotite, 
  and 
  some 
  oligoclase. 
  When 
  sufficiently 
  thin, 
  the 
  slabs 
  

   produce 
  a 
  submetallic 
  sound 
  upon 
  being 
  struck. 
  Descending 
  with 
  the 
  

   stream 
  we 
  find 
  ourselves 
  in 
  the 
  low 
  bluffs, 
  characteristic 
  of 
  the 
  western 
  

   border 
  of 
  tl^e 
  San 
  Luis 
  Valley. 
  Their 
  strata 
  show 
  a 
  general 
  dip 
  to 
  the 
  

   eastward, 
  which 
  here 
  is 
  changed 
  by 
  a 
  slight 
  one 
  to 
  the 
  north. 
  On 
  one 
  

   of 
  the 
  rounded 
  bluffs 
  station 
  14 
  (9,629 
  feet) 
  was 
  located. 
  Its 
  summit 
  

   is 
  formed 
  by 
  a 
  capping 
  of 
  black 
  vesicular 
  basalt, 
  containing 
  small 
  frag- 
  

   ments 
  of 
  a 
  very 
  yellow 
  olivine. 
  On 
  account 
  of 
  the 
  commanding 
  view, 
  

   this 
  point 
  had 
  been 
  utilized 
  as 
  a 
  " 
  lookout 
  " 
  by 
  the 
  Indians, 
  and 
  we 
  

   found 
  the 
  low 
  circle 
  of 
  stones 
  intended 
  to 
  shield 
  the 
  sentinel 
  from 
  

   observation. 
  

  

  Near 
  the 
  San 
  Francisco 
  heads 
  Eio 
  Alamosa. 
  From 
  the 
  northward 
  to 
  

   the 
  entrance 
  of 
  the 
  Alamosa 
  into 
  San 
  Luis 
  valley 
  the 
  eastern 
  border 
  of 
  

   the 
  Sawatch 
  Eange 
  has 
  been 
  formed 
  by 
  trachytic 
  bluffs. 
  Here, 
  how- 
  

   ever, 
  this 
  changes. 
  Station 
  101 
  is 
  located 
  at 
  an 
  elevation 
  of 
  9,627 
  feet, 
  

   and 
  forms 
  a 
  prominent 
  hill 
  on 
  the 
  west 
  side 
  of 
  the 
  valley 
  immediately 
  

   north 
  of 
  the 
  Alamosa. 
  This 
  is 
  composed 
  of 
  trachyte, 
  but 
  south 
  of 
  it 
  

   the 
  more 
  recent 
  basalt 
  sets 
  in. 
  So 
  far 
  as 
  could 
  be 
  determined, 
  the 
  lat- 
  

   ter 
  is 
  unconformable 
  with 
  the 
  former 
  at 
  this 
  point. 
  The 
  Alamosa 
  heads 
  

   at 
  station 
  19, 
  a 
  prominent 
  rough 
  mountain 
  in 
  the 
  trachytic 
  area, 
  rising 
  

   to 
  an 
  elevation 
  of 
  13,323 
  feet. 
  A 
  part 
  of 
  the 
  Alamosa 
  drainage 
  heads 
  

   in 
  the 
  Summit 
  district, 
  and 
  some 
  of 
  the 
  mines 
  there 
  are 
  located 
  within 
  

   its 
  limits. 
  Reaching 
  the 
  valley, 
  the 
  river 
  flows 
  first 
  through 
  a 
  small 
  

   outcrop 
  of 
  the 
  trachytic 
  conglomerate, 
  and 
  then 
  enters 
  a 
  broad 
  caiion 
  

   walled 
  in 
  on 
  either 
  side 
  by 
  basalt, 
  but 
  having 
  a 
  flat 
  bottom 
  that 
  is 
  util- 
  

   ized 
  for 
  agricultural 
  purposes 
  by 
  Mexican 
  settlers. 
  Rio 
  la 
  Jara 
  joins 
  the 
  

   Alamosa 
  in 
  San 
  Luis 
  Valley. 
  The 
  basalt 
  of 
  this, 
  as 
  well 
  as 
  of 
  the 
  border 
  

   of 
  the 
  mountains 
  farther 
  south, 
  covers 
  in 
  an 
  almost 
  continuous 
  layer 
  the 
  

   prevalent 
  trachyte 
  of 
  the 
  region. 
  It 
  shows, 
  near 
  its 
  western, 
  highest 
  edge, 
  

   an 
  easterly 
  dip 
  of 
  about 
  7°, 
  which 
  gradually 
  diminishes 
  as 
  it 
  approaches 
  

   the 
  plain, 
  and 
  eventually 
  enters 
  it. 
  There 
  it 
  forms 
  the 
  bottom 
  of 
  the 
  val- 
  

   ley 
  for 
  some 
  distance, 
  until 
  it 
  is 
  covered 
  by 
  the 
  drift. 
  Wherever 
  branches 
  

   of 
  the 
  stream 
  come 
  from 
  the 
  mountains, 
  they 
  have 
  cut 
  through 
  the 
  

   basalt 
  into 
  the 
  trachyte 
  or 
  trachytic 
  conglomerate, 
  so 
  that 
  the 
  first 
  will 
  

   then 
  only 
  be 
  found 
  as 
  a 
  capping, 
  covering 
  the 
  bluffs 
  that 
  have 
  been 
  

   produced 
  by 
  erosion 
  of 
  the 
  continuous 
  eastward-sloping 
  bench. 
  Identi- 
  

   cal 
  with 
  the 
  occurrence 
  of 
  the 
  basalt 
  here 
  is 
  that 
  on 
  the 
  drainage 
  of 
  

   Rio 
  Conejos, 
  farther 
  south. 
  It 
  heads 
  along 
  the 
  continental 
  divide 
  in 
  

   numerous 
  small 
  branches, 
  west 
  of 
  station 
  86, 
  which 
  we 
  named 
  Conejos 
  

   Peak. 
  This 
  mountain 
  is 
  13,183 
  feet 
  above 
  sea-level, 
  affords 
  an 
  excellent 
  

   landmark, 
  and 
  is 
  entirely 
  surrounded 
  by 
  drainage 
  belonging 
  to 
  the 
  

   river 
  of 
  the' 
  same 
  name. 
  Receiving 
  its 
  largest 
  tributary, 
  Rio 
  San 
  An- 
  

   tonio, 
  from 
  the 
  southwest, 
  the 
  Conejos 
  finds 
  its 
  course 
  through 
  tbe 
  wide- 
  

   spread 
  basalt 
  immediately 
  after 
  leaving 
  the 
  mountains. 
  The 
  most 
  west- 
  

   erly 
  appearance 
  of 
  the 
  basalt 
  is 
  observed 
  on 
  station 
  88, 
  (12,181 
  feet,) 
  

   where 
  it 
  occurs 
  as 
  the 
  capping 
  of 
  a 
  trachytic 
  plateau 
  of 
  small 
  extent, 
  

   11 
  G 
  s 
  

  

  