292 



University of California Publications in Geology [Vol. 8 



The following terranes were recognized in this area : 



(1) A basement complex of schists, marble and limestone of pos- 

 sible Palaeozic age, and intrusive granite of unknown age (oldest 

 member of the section). 



(2) The Martinez Group, consisting of two divisions: (a) a lower 

 predominantly sandstone member, and (b) an upper predominantly 

 shale member. This group rests upon the eroded surface of the base- 

 ment complex on the north side of Pinyon Ridge. It is of lower 

 Eocene age, its basal portion yielding a fauna characteristic of that 

 horizon. 



(3) Miocene ( ?) strata, a thick series of apparently land-laid 

 deposits, in part typical fanglomerates. This formation rests with 

 well-marked unconformity upon the Martinez. 



(4) An andesitic lava flow of later age than the Miocene (?) for- 

 mation. 



(5) A formation of Pleistocene ( ?) age deposited unconformably 

 upon the older beds. 



BASEMENT COMPLEX 



On the outer edge of the mountains, on the border of the desert 

 were found what appear to be the oldest rocks in the area, limestone 

 and schists which were intruded by granite. The limestone is a 

 bluish gray rock of fine texture and in places still exhibits stratifica- 

 tion. Occasionally it is found to be altered to marble. The schists 

 associated with it are fine-grained and micaceous. This series may 

 be the correlative of Hershey's 2 Oro Grande series, of the Mohave 

 desert forty miles northeast of this locality. This limestone and schist 

 series has been brought upward by movements along two very recent 

 faults, the Antelope Valley and the Rock Creek faults of the San 

 Andreas rift. 



The main mass of the range consists of granitoid rocks and asso- 

 ciated schists, and in the area mapped, it is rather sharply set off 

 from the sedimentaries along the Punch-bowl fault. The granite 

 appears to be intruded into a much altered hornblende schist. Along 

 the Punch-bowl fault a dike of aplite in the granite is a very prominent 

 feature of the complex. 



2 ITersliey, O., Some crystalline rocks of southern California, Am. Geol., vol. 

 29, pp. 286-287, 1902. 



