if 
242  CONTRIBUTIONS    TO    ECONOMIC    GEOLOGY,  1903.  [bull. 225. 
Deer    Creek,  on    the   west,  from    that   of    Hawk    Canyon,  on    the 
east. 
The  western  border  of  the  eoal  field  is,  in  a  general  way,  formed  by 
a  range  of  mountains  which  lies  parallel  to  and  east  of  the  San  Pedro 
Valley.  South  of  Aravaypa  Creek  this  range  is  high,  and  it  is  known 
by  the  name  of  the  Caliuro  Range.  Between  Aravaypa  Creek  and 
Gila  River  the  range  is  inconspicuous,  and  it  is  represented  only  by  a 
lava-capped  mesa  just  north  of  Aravaypa  Creek  and  by  Saddle  Moun- 
tain, near  Gila  River.  The  topography  of  the  coal  field  is  varied,  but, 
broadly  considered,  it  is  a  topographic  basin  surrounded,  except  on  the 
west,  by  more  rugged  country.  The  basin  of  Deer  Creek  is  particu- 
larly flat  in  the  Upper  and  Lower  coal  fields.  These  are  separated  by 
a  more  rugged  region,  and  between  the  Lower  field  and  Gila  River  the 
topography  is  rough  and  mountainous. 
The  coal  field  occupies  an  irregular  synclinal  basin  between  the 
Mescal  Range  on  the  north  and  an  unnamed  ridge  on  the  south,  which 
separates  the  basins  of  Deer  and  Ash  creeks.  Within  about  5  miles 
of  Gila  River  the  range  lying  on  the  south  side  of  the  coal  field  turns 
to  the  southwest  and  merges,  in  a  general  way,  with  the  northern 
extension  of  the  Caliuro  Range.  The  major  portion  of  the  coal  field 
is  drained  by  Deer  Creek,  but  the  coal-bearing  rocks  extend  to  the 
southwest  beyond  Saddle  Mountain;  and  this  part  of  the  field  lies  j 
within  the  drainage  basin  of  Ash  Creek.  The  coal-bearing  rocks 
undoubtedly  extend  to  the  northwest  be}^ond  Gila  River,  but  they  are 
so  broken  and  disturbed  by  volcanic  rocks  that  presumably  the  coal  is 
of  no  value,  and  it  is  not  represented  on  the  map. 
The  field  extends  10  or  12  miles  in  an  east-west  direction,  and  it  has 
a  known  breadth  of  3  or  4  miles  in  the  Deer  Creek  Basin.  As  previ- 
ously stated,  the  coal-bearing  rocks  are  found  in  the  Ash  Creek  Basin, 
and  it  is  possible  that  the  coal  field  may  be  extended  to  the  outcrop  of 
the  limestone  west  of  Saddle  Mountain. 
Coal  beds  are  also  reported  as  occurring  in  Hawk  Canyon,  where 
the  coal-bearing  rocks  appear  on  the  north  side  of  the  great  broken 
anticline  forming  the  Mescal  Range,  and  it  seems  possible  that  similar 
deposits  may  be  found  in  the  basin  of  upper  Ash  Creek  and  in  the 
great  Aravaypa  Valley  to  the  southeast. 
This  paper  is  the  result  of  a  rapid  reconnaissance  of  the  field  during 
the  past  autumn.  The  time  was  too  short  to  permit  of  a  detailed 
study  of  the  field  relations  of  all  of  the  rocks  involved,  but  through 
the  kindness  of  Mr.  N.  H.  Mellor,  superintendent  of  the  Saddle 
Mountain  Mining  Company,  who  has  given  much  attention  to  the 
geology  of  the  region,  the  writer  was  enabled  to  see  many  of  the 
critical  points  and  to  present  the  following  brief  outline  of  its  most 
important  geologic  features. 
