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  SANTA 
  M.\ 
  IMA 
  OIL 
  DISTRICT, 
  CALIFORNIA. 
  

  

  disturbed 
  thai 
  little 
  clew 
  as 
  to 
  their 
  structure 
  can 
  be 
  obtained, 
  and 
  

   so 
  local 
  in 
  extent 
  that 
  no 
  attempt 
  has 
  been 
  made 
  in 
  mapping 
  to 
  

   differentiate 
  them 
  from 
  the 
  accompanying 
  serpentine. 
  

  

  KNOXVILLE 
  FORMATION 
  (LOWEB 
  CRETACEOUS). 
  

  

  Several 
  small 
  areas 
  of 
  sedimentary 
  rock 
  occur 
  which 
  can 
  be 
  defi- 
  

   nitely 
  assigned 
  on 
  fossil 
  evidence 
  to 
  the 
  Knoxville, 
  or 
  lower 
  Cretaceous. 
  

  

  The 
  two 
  most 
  important 
  are 
  north 
  of 
  Mount 
  Lospe, 
  in 
  the 
  Oasmalia 
  

   Hills. 
  The 
  rock 
  is 
  chiefly 
  dark-colored, 
  unaltered 
  argillaceous 
  shale, 
  

   such 
  as 
  is 
  characteristic 
  of 
  the 
  Knoxville 
  throughout 
  its 
  wide 
  area 
  

   of 
  distribution 
  in 
  the 
  California 
  Coast 
  Ranges. 
  Sandstone 
  and 
  con- 
  

   glomerate 
  occur 
  in 
  lesser 
  amounts. 
  Brownish-yellow 
  sandstone, 
  

   similar 
  to 
  that 
  common 
  in 
  the 
  Knoxville 
  in 
  the 
  Coast 
  Ranges 
  several 
  

   hundred 
  miles 
  farther 
  north, 
  occurs 
  on 
  the 
  border 
  of 
  an 
  irregular 
  

   area 
  of 
  diabase 
  on 
  Tepusquet 
  Creek, 
  in 
  the 
  San 
  Rafael 
  Mountains, 
  

   and 
  contains 
  the 
  characteristic 
  Knoxville 
  fossil 
  Aucella 
  piocMi 
  Gabb 
  

   (PI. 
  XIII, 
  figs. 
  1, 
  2, 
  3a, 
  3b, 
  p. 
  128). 
  The 
  rock 
  is 
  present 
  only 
  in 
  very 
  

   small 
  patches, 
  and 
  seems 
  to 
  have 
  been 
  brought 
  up 
  from 
  below 
  by 
  the 
  

   diabase 
  intrusion. 
  The 
  Knoxville 
  was 
  recognized 
  in 
  one 
  other 
  place 
  

   in 
  the 
  San 
  Rafael 
  Mountains 
  a 
  few 
  miles 
  north 
  of 
  Zaca 
  Lake, 
  at 
  the 
  

   base 
  of 
  the 
  series 
  mapped 
  as 
  pre-Monterey, 
  where 
  also 
  it 
  contains 
  

   Aucella 
  piochii. 
  It 
  is 
  very 
  likely 
  that 
  a 
  portion 
  of 
  the 
  areas 
  mapped 
  

   as 
  pre-Monterey 
  belongs 
  to 
  the 
  lower 
  Cretaceous, 
  but 
  it 
  is 
  not 
  prob- 
  

   able 
  that 
  the 
  whole 
  does. 
  

  

  PRE-MONTEREY 
  ROCKS. 
  

  

  Two 
  large 
  areas 
  of 
  sedimentary 
  rocks 
  whose 
  age 
  has 
  not 
  been 
  

   determined 
  otherwise 
  than 
  that 
  they 
  are 
  older 
  than 
  the 
  Monterey 
  

   occur 
  in 
  the 
  San 
  Rafael 
  Mountains. 
  They 
  are 
  mapped 
  as 
  pre- 
  

   Monterey 
  rocks. 
  It 
  is 
  probable 
  that 
  strata 
  of 
  Knoxville 
  (lower 
  

   Cretaceous) 
  age 
  occur 
  at 
  the 
  base 
  of 
  the 
  series 
  in 
  those 
  areas 
  and 
  

   that 
  the 
  higher 
  portions 
  represent 
  either 
  the 
  upper 
  Cretaceous 
  or 
  

   the 
  Eocene, 
  or 
  both. 
  Detailed 
  work 
  was 
  left 
  until 
  another 
  time. 
  

  

  The 
  larger 
  of 
  these 
  two 
  areas 
  occupies 
  the 
  northeast 
  corner 
  of 
  the 
  

   region 
  shown 
  on 
  the 
  map, 
  and 
  is 
  about 
  60 
  square 
  miles 
  in 
  extent. 
  

   The 
  other 
  lies 
  on 
  the 
  northeastern 
  slope 
  of 
  the 
  high 
  ridge 
  north 
  of 
  

   Zaca 
  Lake. 
  In 
  these 
  areas 
  are 
  exposed 
  a 
  great 
  series 
  of 
  thin-bedded, 
  

   dark-colored, 
  locally 
  greenish 
  shale 
  alternating 
  with 
  more 
  massively 
  

   bedded 
  sandstone, 
  which 
  is 
  in 
  places 
  of 
  a 
  very 
  granitic 
  nature. 
  Con- 
  

   glomerate, 
  much 
  of 
  it 
  plainly 
  evidencing 
  its 
  origin 
  from 
  granite, 
  

   occurs 
  in 
  minor 
  horizons. 
  Knoxville 
  fossils 
  were 
  found 
  in 
  a 
  gritty 
  

   greenish 
  sandstone 
  near 
  the 
  lowest 
  portion 
  of 
  this 
  pre-Monterey 
  

   terrane, 
  about 
  2 
  miles 
  north 
  of 
  Zaca 
  Lake. 
  The 
  higher 
  portion 
  seems 
  

   to 
  be 
  the 
  continuation 
  of 
  a 
  formation 
  in 
  San 
  Luis 
  Obispo 
  County 
  that 
  

  

  