SALT    LAKE    OIL    FIELD,    LOS    ANGELES,    CAL.  359 
(fact  that  the  conditions  favorable  to  the  accumulation  of  the  brea  have  been  in  existence 
here  at  least  since  the  middle  or  latter  part  of  the  Pleistocene  epoch.  Heavy  oil  exudes 
from  the  banks  of  the  lagoon  and  from  some  of  the  minor  brea  pits,  while  the  constant 
escape  of  natural  gas  is  evidenced  by  the  continuous  streams  of  bubbles  which  rise  to  the 
(surface  of  the  water  in  the  different  depressions. 
Geology  of  the  wells.— The  wells  usually  penetrate,  for  the  fust  "0  to  100  feel  or  more,  allu- 
i  vium  and  clay,  with  varying  amounts  of  coarse  sand  and  gravel,  representing  the  Pleistocene 
|  covering  of  the  older  formations.  These  deposits  carry  water,  which  in  some  instances  is 
mineralized,  in  one  or  more  of  the  beds.  A  little  heavy  oil  or  asphaltum  is  also  occasionally 
found  in  the  superficial  deposits.  In  fact,  in  some  parts  of  the  field  the  oil  appeals  to 
impregnate  the  soil  and  rocks  "from  the  grass  roots  down."  From  the  Pleistocene  to  the 
first  important  oil  sand  (which  is  struck  at  from  1,000  to  3,000  feet)  the  beds  consist  of 
soft  sandy  shale  ("adobe")  and  clayey  shale,  with  occasional  1  to  6  foot  layers  of  hard 
siliceous  or  calcareous  shale  ("shell")  and  sometimes  a  little  sand  and  gravel.  This  series 
belongs  in  large  part  to  the  Pliocene.  Oil  and  gas,  increasing  in  quantity  downward,  are 
found  in  many  of  the  beds  of  this  series,  the  largest  accumulations  usually  occurring  just 
beneath  the  hard,  impervious  "shell"  layers.  Salt  water  is  also  encountered  at  various 
depths,  the  more  aqueous  horizons  appearing  at  about  150  feet  above  and  between  950  and 
1,000  feet  above  the  top  of  the  uppermost  productive  sand.  Another  bed  carrying  salt 
water  is  encountered  about  150  feet  below  the  lowest  important  oil  sand.  This  water 
attains  a  temperature  of  110°  in  some  of  the  wells.  The  oil  zone  proper  varies  in  thickness 
from  150  to  nearly  500  feet,  and  consists  of  alternating  thick-bedded  rather  coarse  sand  and 
clayey  shale  and  "shell."  Whether  or  not  the  sand  occurs  as  persistent  layers,  or  rather 
as  lenses,  is  problematical,  although  it  is  highly  probably  that  it  is  present  in  both  forms 
within  the  area  under  discussion.  This  much  is  known,  however,  that  the  uppermost 
important  sand  in  the  wells  oyer  a  large  part  of  the  field  appears  to  occupy  t  he  same  horizon. 
The  lower  limit  of  the  productive  zone  is  usually  a  sterile  white  sand,  sometimes  locally 
hardened,  which  yields,  at  a  depth  of  150  feet  or  more  below  its  fop,  large  quantities  of 
warm  or  hot  salt  water.  One  well,  it  is  said,  struck  some  11°  oil  in  this  lowest  salt-water 
stratum.  A  typical  section  through  the  oil  zone,  where  the  dip  is  approximately  15°,  is  as 
follows: 
Typical  section  of  oil-sand  zone  in  Salt  Lake  field. 
Foot. 
Sandy  shale  ( ' ' adobe ") 300+ 
Oil  sand 20 
Clayey  shalo 30 
Oil  sand 10 
Clayey  shale 20 
Oil  sand 20 
Hard  shale 2 
Oil  sand 123 
Tough  brown  shale 10 
Oil  sand 25 
Clayey  shale 10 
Oil  sand 10 
Clayey  shalo 86 
Oil  sand 129 
White  sand 150 
Sand  with  salt  water  (hot)  and  occasionally  some  11°  oil 200+ 
Total  productive  sand 337 
Structure. — Owing  to  the  almost  complete  absence  of  surface  evidence  in  the  immediate 
vicinity,  the  determination  of  the  local  structure  of  the  Salt  Lake  field  rests  largely  on  the 
interpretation  of  the  well  logs.  All  of  these,  unfortunately,  were  not  available  at  the  time 
of  the  writer's  visit  to  the  field,  so  that  the  conclusions  reached,  although  probably  cornet 
in  the  main,  lack  that  detail  and  definiteness  which  is  so  desirable  in  an  economic  report  of 
this  sort. 
