Page 15 - muehlberger1954
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                      Between Newhall  and Castaic  in the  eastern part of the  Ventura

          basin,  the  San Gabriel  fault,  one  of the  major faults  of  southern Califor-


          nia,  trends northwest across the  basin and  marks  a  significant  strati-

          graphic  break between the  western and easternmost portions of the  basin.

          This  fault  marks the  eastern limit of  both oil  production and the  thick


          section of marine  sediments.  Except for  minor  amounts  of marine

          sediments,  the  easternmost Ventura basin is underlain by a  thick  series


          of  nonmarine  sediments  and  interlayered volcanic  rocks.           To  replace

          the  cumbersome  term,  easternmost Ventura basin,  Bailey and Jahns


          (1954)  have  suggested the  name  Soledad basin,  which  implies  a  sharper

          distinction between the  areas  on opposite  sides of the San Gabriel  fault.

          This  study is mainly concerned with the  northern and eastern two-


          thirds of the  Soledad basin (pl.  1).

                      Members  of the  various  railroad,  geological  and  geographical


          surveys  of the  middle  19th Century passed through this  region and made

         many  scattered geological  observations.  The  fir st attempts  at  system-

          atic  analysis of this  region were  made  by Hershey ( 1902a;  19O2b),  who


         briefly described the  major  rock units.  He  named the  Pelona  schist,

          and this  designation  since has  been extended to  other  areas at  some


         · distance  from  the  type  area  in the  Sierra Pelona.  He  also  named

          several other  units,  but these  designations  have  been revised by later

          investigators.     Hershey's oldest Tertiary unit,  the  Escondido  series,


         lies directly on his  probable  pre-Cambrian Gneiss  and Pelona Schist

          series.  His  next younger  Tertiary unit,  the  Mellenia  series,  crops out
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