PETROLEUM  AND  NATURAL  GAS. 
THE  SALT  LAKE  OIL  FIELD  NEAR  LOS  ANGELES,  CAL. 
By  Ralph  Arnold. 
Introduction. — Since  the  completion,  four  years  ago,  of  the  examination  of  the  California 
oil  districts  by  the  late  G.  H.  Eldridge,  one  of  the  most  important  fields  in  the  State  has 
been  developed  near  the  city  of  Los  Angeles.  This  field,  locally  known  as  the  Salt  Lake 
from  its  first  important  producing  company,  has  grown  from  a  position  of  comparative 
insignificance  in  1902  to  that  of  possibly  the  premier  field  of  southern  California  in  1905. 
Location  and  topography. — The  Salt  Lake  oil  field  occupies  an  area  approximately  a  mile 
square,  7  miles  west  of  the  business  portion  of  Los  Angeles,  Cal.  (see  fig.  12).  The  field  is  a  part 
of  the  Los  Angeles-Santa  Monica  plain,  which  extends  southward  with  a  gradually  lessening 
slope  from  the  base  of  the  Santa  Monica  Range  toward  the  hills  southwest  of  Los  Angeles. 
With  the  exception  of  a  few  unimportant  ravines  which  run  in  a  general  southwesterly 
direction  across  the  plain  and  an  extensive  slope  which  descends  gradually  from  the  field 
northwestward  toward  Sherman,  there  is  little  to  break  the  topographic  monotony  in  the 
vicinity  of  the  wells.  A  small  artificial  lagoon,  made  by  the  removal  of  large  quantities  of 
brea,  occupies  a  depression  about  75  by  150  yards  laear  the  center  of  the  southern  part  of 
the  field.     Reference  will  be  made  to  this  lagoon  later  in  the  discussion.  , 
Geologic  formations. — Alluvium  and  Pleistocene  deposits  of  gravel,  sand,  and  clay  cover 
the  plain  in  the  region  of  the  Salt  Lake  field,  but  surface  outcrops  of  other  beds  are  to  be 
found  no  nearer  than  about  2  miles  from  the  present  developed  territory.  The  well  logs 
and  a  study  of  the  adjacent  region  indicate,  however,  that  the  formations  involved  in  the 
geology  of  this  field  include  at  least  a  part  of  those  exposed  to  the  east,  in  the  vicinity  of 
the  Los  Angeles  city  field,  and  consist  of  (a)  2,000+  feet  of  lower  Miocene  sandstone,  (b) 
2,000d=  feet  of  middle  and  possibly  upper  Miocene  shales  and  thin-bedded  sandstones, 
(c)  2,000+  feet  of  Pliocene  clayey  and  sandy  shale,  sandstone,  and  gravel,  and  (d)  an 
unconformable  capping  of  Pleistocene  gravel,  sand,  and  clay  varying  in  thickness  from 
40  to  at  least  100  feet  or  more,  the  whole  covered  by  alluvium. 
The  lower  Miocene  sandstones  are  coarse,  arkose,  and  heavy  bedded,  gray  to  rusty  brown 
in  color,  sometimes  concretionary  in  structure,  and  often  jointed.  They  are  interbedded 
at  irregular  intervals  by  smaller  amounts  of  dark-colored  earthy  and  lighter  siliceous  shales. 
Toward  the  top  of  the  series,  however,  the  shales  become  relatively  more  abundant.  No 
sharp  line  of  demarcation  separates  the  sandstones  from  the  overlying  series,  which  con- 
sists largely  of  shales  of  middle  and  possibly  upper  Miocene  age.  The  lower  1,000  feet  of 
this  series  are  made  up  of  hard,  white,  thinly  laminated  siliceous  shale,  occurring  in  bands 
200  feet  or  less  in  thickness,  alternating  with  thinner  bands  of  sandstone  similar  to  those 
of  the  lower  Miocene.  About  1,000  feet  of  soft,  thin-bedded  sandstone  and  sandy  shale, 
with  some  hard  siliceous  members  and  coarser  sandstone  toward  the  top,  overlie  the  white- 
shale  beds.  The  upper  portion  of  this  upper  shale  series,  and  possibly  some  of  the  strata  of 
the  superjacent  formation  yield  the  oil,  the  most  productive  sands  appearing  to  lie  beneath 
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