296 University of California Publications in Geology [Vol. 8 



The basal member consists of fifty to one hundred feet of fanglomerate 

 derived from the underlying Martinez sandstone. This fanglomerate 

 consists of very angular blocks, some of which are eighteen inches in 

 greatest dimension. This basal member rests unconformably upon 

 the Martinez sandstone. This is shown by marked differences in both 

 dip and strike between the two terranes, and by the occurrence in the 

 middle of the Devil's Punch-bowl of a boulder in the conglomerate 

 containing Turritella ■pachecoensis, a characteristic Martinez fossil. 

 The Miocene ( ?) strata, which have an estimated thickness of from four 

 thousand to five thousand feet, consist of a basal fanglomerate and 

 alternating strata of coarse conglomeritic sandstone, clay, black 

 lignitic shale, and fanglomerate. The series does not appear to be 

 marine but is, at least in part, a land-laid deposit and in part 

 lacustrine. This formation may be identical with that exposed in 

 Cajon Pass judging from the description of these beds by Johnson, 3 

 and by exposures seen from the train. The Eseondido formation of 

 Hershey may also be an equivalent. Direct areal connection with other 

 occurrences of this formation is impossible owing to the intervening 

 areas of granite on the west and southeast. Until determinative 

 fossils have been found in these three localities their relations to each 

 other and their age will remain unsettled. The writer is inclined to 

 regard the formation as Miocene in age. This opinion is based upon 

 a study of the known distribution of the upper Eocene, the Tejon in 

 southern California, and upon the diastrophic record. The Tejon 

 of the Santa Ana Mountains and in the vicinity of San Diego were 

 both apparently deposited under stranddike conditions. No Tejon 

 sediments have been recognized around Los Angeles. The strand line 

 of the Tejon sea was probably west of the present site of Los Angeles, 

 and west of the Rock Creek area. 



ANDESITIC LAVA FLOW 



In the gravels of the Pleistocene ( ?) formation were found certain 

 boulders of andesite which were evidently not contributed by any 

 formation within the area mapped in the neighborhood of Rock Creek. 

 No boulders of this rock were found in the conglomerates of the 

 Miocene ( ?) beds. Evidently an outpouring of lava occurred after the 

 deposition of the Miocene ( ?), but erosion removed it from the vicinity 

 of Rock Creek before the Pleistocene beds were laid down. In a brief 



3 Johnson, H. R., Water resources of Antelope Valley, California, U. S. G. S., 

 Water Supply Paper 278, p. 30, 1911. 



