Fig. 1. A geological map of a portion of the Rock Creek Quadrangle, Los Angeles County, California. 

 l/r. Is, Basement Complex; Tmz, Martinez Group; Tpb, Miocene(?) formation; Pp, Pleistocene ( ?) 

 formation ; al. Alluvium. Adapted from the U. S. Geological Survey topographic sheet. Scale, 1 inch = 1 mile. 



