Page 4 - macneill1947
P. 4

2.




                                            AB$TRAQT



                      Six  formations  of  Tertiary  and  Quaternary  Age  are

         present  south  of  the  Santa  Clara  River  in  the  Easternmost

         Ventura  .Basin.

                      The  upper Miocene  non-marine  Mint  Canyon  formation  is

         suooessively  overlain  by  the  uppermost  .Miocene  marine  ''Modelo"


         formation,  the  lower  Pliocene  marine  Pico  formation,  the

         Pliooene-Pleistooene  non-marine  Saugus  formation,  and  by

         Pleistocene  terrace  deposits  and  Heoent  alluvium.  Angular

         unoonformities  characterize  most  of  the  boundaries  between

         these  formations,  but  disconformable  relationships  appear  to

         exist  locally.

                      As  a  result  o1'  two  or  more  major  periods  of  defor-


         mation,  the  rocks  are  highly  folded,  with  broken  anticlines

         and  dips  that  vary  from  horizontal  to  ve,rtical.  Overturning

         ooours  at  least  at  one  place.  Compressive  stresses  from  the

         north  appear  to  have  been  the  most  active  agents  of  deformation;

         but  the  block-type  San  Gabriel  fault.  which  runs  through  the

         Southern  part  of  the  Humphreys  Station  area,  may  have  had  some

         tilting effect  upon  the  beds  throughout  this  whole  region.

                      In  general,  the  structural  trend  is  northwest-

         southeast.  Broad  folds  in  the  Mint  Canyon  fonnation  plunge


         northwestward  at  low  to  moderate  angles.  Post-Modelo  thrust-

         ing  from  the  north  has  developed minor  folds  on  the  limbs  of

         the  mqor  folds.  Superimposed  on  the  highly  folded  formations

         are  the  later  formations,  themselves  slightly  folded.

                      As  a  result  of  ~uaternary  erosion,  the  topography  is
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