Page 3 - muehlberger1954
P. 3



                      The Soledad basin is  situated north of the San Gabriel

         Mountains,  in Los Angeles County,  California,  and its  center  is  about

         35  miles north of the Los Angeles  civic  center.  Roughly an elongate

         parallelogram in  shape,  this  basin has  dimensions of about ten by

         thirty miles,  with the  longer  dimension oriented  east-west.  The  Sierra

         Pelona and the San Gabriel Mountains  form  the  northern and  southern

         boundaries,  respectively.  The San Andreas fault and the San Gabriel

         fault,  both of which trend northwest in this  region,  bound the  basin on

         its northeast and  southwest borders,  respectively.            Only the  northern

         part of the  basin is  discussed in this  paper.

                      The  pre-Cretaceous Pelona  schist,  the oldest unit in the  map

         area,  is  a  thick sequence of muscovite  schist,  chlorite-muscovite

         schist and actinolite-chlorite  schist with  rare layers of quartzite  and

         limestone.  This  unit underlies  the Sierra Pelona,  an  elongate mountain

         mass which trends  east-west.  Granitic  intrusive  rocks of  probable

         late  Jurassic  age underlie  a  complex  section of  Tertiary rocks  in mo st

         of the  eastern Soledad basin.  Gneisses,  some of which may represent

        . highly injected Pelona  schist,  also  are present in a  belt that in  general

         trends  parallel to  the Sierra Pelona~

                      In  general,  the  sedimentary beds  exposed at the  surface are

         younger  from  east to  west in the Soledad basin.  The  marine  Martinez

         formation of Paleocene age  is the  oldest  sedimentary unit in the  region.
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