﻿10S 
  SANTA 
  MAH1A 
  OIL' 
  DISTRICT, 
  CALIFORNIA, 
  

  

  this 
  work 
  nearly 
  all 
  of 
  the 
  territory 
  of 
  the 
  hills 
  between 
  San 
  Luis 
  

   Obispo 
  ('reek 
  and 
  the 
  Arroyo 
  Grande 
  Valley, 
  with 
  the 
  exception 
  of 
  

   a 
  rather 
  small 
  area 
  of 
  Monterey 
  volcanic 
  ash, 
  shale, 
  and 
  diatoma- 
  

   ceous 
  earth 
  north 
  of 
  Pismo, 
  is 
  covered 
  by 
  the 
  Pismo 
  formation. 
  

   This 
  formation 
  is 
  composed 
  of 
  sandstone, 
  some 
  of 
  which 
  is 
  asphalt 
  ic, 
  

   and 
  cherty 
  diatomaceous 
  beds, 
  and 
  is 
  the 
  equivalent 
  of 
  the 
  lower 
  

   part 
  of 
  the 
  Fernando 
  formation 
  as 
  described 
  for 
  the 
  hills 
  adjacent 
  to 
  

   the 
  south 
  side 
  of 
  the 
  Santa 
  Maria 
  Valley. 
  The 
  Pismo 
  is 
  unconform- 
  

   able 
  underlain 
  by 
  the 
  Monterey 
  shale, 
  which 
  outcrops 
  on 
  either 
  side 
  

   of 
  it. 
  

  

  STRUCTURE. 
  

  

  According 
  to 
  Fairbanks, 
  the 
  Pismo 
  area 
  forms 
  a 
  low 
  syncline, 
  

   striking 
  northwest 
  and 
  southeast, 
  its 
  flanks 
  resting 
  against 
  the 
  up- 
  

   turned 
  Monterey. 
  

  

  OCCURRENCE 
  OF 
  THE 
  OIL. 
  

  

  The 
  oil 
  is 
  derived 
  from 
  a 
  great 
  thickness 
  of 
  productive 
  sands 
  which 
  

   probably 
  represent 
  the 
  base 
  of 
  the 
  Pismo 
  and 
  which 
  rest 
  upon 
  the 
  

   upturned 
  and 
  more 
  or 
  less 
  contorted 
  shale 
  of 
  the 
  Monterey. 
  Its 
  

   occurrence 
  in 
  beds 
  occupying 
  a 
  s} 
  T 
  nclinal 
  position 
  is 
  worthy 
  of 
  note, 
  

   as 
  ordinarily 
  synclines 
  are 
  not 
  highly 
  productive. 
  The 
  Monterey 
  is 
  

   the 
  oil-bearing 
  formation 
  in 
  the 
  Santa 
  Maria 
  district, 
  and 
  it 
  is 
  the 
  

   ultimate 
  source 
  of 
  the 
  oil 
  in 
  this 
  field 
  also. 
  The 
  migration 
  of 
  the 
  oil 
  

   probably 
  took 
  place 
  along 
  joint 
  cracks 
  in 
  the 
  shale, 
  as 
  was 
  the 
  case 
  

   with 
  the 
  asphaltum 
  in 
  the 
  Santa 
  Maria 
  and 
  other 
  fields. 
  The 
  oil, 
  on 
  

   reaching 
  the 
  upper 
  limit 
  of 
  the 
  shale 
  passed 
  across 
  the 
  plane 
  of 
  uncon- 
  

   formity 
  and 
  accumulated 
  beneath 
  an 
  impervious 
  shale 
  in 
  the 
  porous 
  

   sands 
  at 
  the 
  base 
  of 
  the 
  Pismo. 
  Where 
  this 
  porous 
  layer 
  approaches 
  

   the 
  surface 
  the 
  more 
  volatile 
  parts 
  of 
  the 
  oil 
  have 
  escaped 
  and 
  there 
  

   remains 
  nothing 
  but 
  the 
  bitumen, 
  while 
  the 
  more 
  deeply 
  covered 
  

   sands 
  retain 
  the 
  oil 
  in 
  its 
  lighter 
  and 
  liquid 
  state. 
  The 
  migration 
  of 
  

   the 
  oil, 
  as 
  in 
  every 
  similar 
  case 
  coming 
  under 
  the 
  notice 
  of 
  the 
  writers, 
  

   has 
  been 
  accompanied 
  by 
  a 
  loss 
  of 
  its 
  volatile 
  constituents 
  and 
  a 
  con- 
  

   sequent 
  lowering 
  of 
  the 
  gravity. 
  This 
  is 
  evidenced 
  by 
  the 
  fact 
  that 
  

   although 
  the 
  gravity 
  of 
  the 
  oil 
  from 
  the 
  Monterey 
  formation 
  in 
  the 
  

   Santa 
  Maria 
  field 
  averages 
  about 
  25°, 
  that 
  from 
  the 
  Pismo 
  in 
  the 
  

   Arroyo 
  Grande 
  field 
  is 
  only 
  14°. 
  

  

  CONCLUSIONS 
  REGARDING 
  FUTURE 
  DEVELOPMENT. 
  

  

  It 
  seems 
  almost 
  certain 
  that 
  considerable 
  portions 
  of 
  the 
  Pismo 
  

   formation 
  toward 
  the 
  middle 
  of 
  the 
  area 
  northwest 
  and 
  north 
  of 
  

   Arroyo 
  Grande 
  will 
  be 
  found 
  to 
  be 
  oil 
  producing. 
  This 
  conclusion 
  is 
  

   based 
  on 
  the 
  assumption 
  that 
  the 
  Pismo 
  of 
  this 
  region 
  is 
  underlain 
  

  

  