574  CONTRIBUTIONS    TO    ECONOMIC    GEOLOGY,  1904.         [bull.  260. 
mountains  are  10  miles  wide,  but  they  converge  in  a  wedge-shaped 
form  and  abruptly  terminate  about  10  miles  south  in  a  precipitous 
cliff  called  Guadalupe  Point.  El  Capitan  Peak,  having  an  elevation 
of  approximately  8,500  feet,0  is  one-fourth  of  a  mile  north  of  Guada- 
lupe Point,  and  is  thought  to  be  the  highest  point  in  Texas. 
The  Delaware  Mountains  are  the  southern  extension  of  the  Guada- 
lupes.  They  extend  northwest-southeast  uninterruptedly  for  about 
40  miles,  beyond  which  they  are  considerably  dissected  and  form  an 
irregular,  unnamed  highland  mass  which  reaches  almost  to  the  Texas 
and  Pacific  Railway.  These  mountains  constitute  a  typical  cuesta. 
They  have  a  southwestward- facing  scarp  approximately  2,000  feet 
high,  from  the  crest  of  which  the  surface  slopes  gradually  north- 
eastward, conforming  approximately  with  the  dip  of  the  underlying 
rocks.  Along  the  western  face  of  the  escarpment  there  is  a  belt  of 
dissected  foothills,  but  no  drainage  way  cuts  across  the  escarpment 
in  the  Delaware  Mountains  proper.  At  the  southern  extremity  of 
the  mountains  the  escarpment  becomes  indistinct,  and  a  longitudinal 
valley  extends  parallel  with  the  axis  of  a  low  anticlinal  fold. 
The  streams  that  drain  the  Delaware  Mountains  are  mainly  con- 
sequent and  flow  down  the  slope  of  the  monocline.  Delaware  Creek 
and  the  valleys  at  the  heads  of  Salt  and  Cottonwood  draws  are  the 
chief  waterways,  although  no  stream  except  Delaware  Creek  below 
Delaware  Springs  is  perennial.  Some  lateral  valleys  are  developed 
which  trend  approximately  parallel  to  the  strike  of  the  rocks,  Wild 
Horse  Draw  being  a  typical  example.  Near  the  crest  of  the  moun- 
tains the  valleys  are  steep  and  narrow,  but  eastward  they  broaden  out. 
Salt  basin,  which  is  one  of  the  prominent  debris-filled  intermontane 
valleys  of  the  trans-Pecos  country,  lies  west  of  the  Guadalupe-Dela- 
ware Mountains.  It  has  the  characteristic  northwest-southeast 
trend  and  is  over  150  miles  long.  The  area  under  consideration 
includes  70  miles  of  the  linear  extent  of  the  Salt  basin,  which  here 
ranges  from  8  to  20  miles  in  width,  averaging  about  15  miles.  The 
Salt  basin  is  a  typical  closed  basin,  with  no  drainage  outlet.  The 
center  is  about  25  miles  north  of  Van  Horn,  at  the  base  of  the  Diablo 
Mountains,  where  the  elevation  is  below  3,600  feet.  The  rise  is  very 
gradual  both  to  the  north  and  to  the  south.  Northward  from  the 
center  of  the  basin  to  the  State  line  the  slope  of  the  surface  is  only 
about  2  feet  in  a  mile,  and  the  basin  appears  to  be  flat  in  its  longer 
extent  and  to  rise  only  to  the  adjacent  highlands  on  the  northeast 
and  southwest.  The  surface  is  not  a  level  plain,  but  is  characterized 
by  numerous  hillocks  and  local  depressions.  The  former  are  often 
composed  of  wind-blown  material,  and  the  latter  are  locally  called 
"  lakes,"  though  only  one  contains  a  considerable  body  of  water.     This 
0  Barometric  determination. 
