TERTIARY FAUNAS OF THE PACIFIC COAST 245 



Kettleman Hills in southern Fresno County, CaL, and the Carrizo 

 Creek beds of the Gulf province of southeastern California has led to 

 the correlation of the latter with the former, although the writer's first 

 examination of the Carrizo Creek fossils led to his placing them 

 tentatively in the lower Miocene.' This correlation of the beds with 

 the upper Miocene seems best to fit the conclusions based on other 

 criteria such as faunal relations, character of sediments, sequence of 

 geologic events in this province, etc. 



THE PLIOCENE AND QUATERNARY PERIODS 

 CONDITIONS OF DEPOSITION AND CHARACTER OF SEDIMENTS 



Sedimentation was continuous from the Miocene through the 

 Pliocene and on into the Quaternary over large areas along the 

 Pacific Coast, but there was a marked change in the conditions sur- 

 rounding the deposition at various times within this long period. In 

 a limited coastal belt, marine conditions marked the Pliocene and 

 Quaternary as well as the upper Miocene, while farther inland fresh- 

 water, possibly alternating with short brackish-water or even marine, 

 conditions prevailed during the Pliocene and Quarternary. This 

 change from marine to lacustrine environment in the basin provinces 

 of the Coast Ranges was probably brought about by two causes: 

 first, a gradual elevation of the whole coast, and second, as suggested 

 by Newsom,^ movements along the earthquake rift and other faults 

 in which certain of the blocks were elevated, forming barriers across 

 pre-existing channels between the interior basins and the ocean. 

 Faunal evidence indicates that those basins farthest inland, such 

 as the San Joaquin Valley, became fresh possibly earlier in the Pliocene 

 than those nearer the sea, such as the Santa Clara Valley basin. 



The marine Pliocene deposits consist largely of fine sand and soft 

 shale, and sometimes marl, while the freshwater sediments usually 

 include considerable thicknesses of coarse, more or less incoherent 

 gravels, hardened silt and sands. The maximum thickness of the 

 marine Pliocene is attained in the Merced section immediately 

 south of San Francisco, where approximately 4,000 feet of strata 

 of Pliocene age are exposed. The greatest thickness of freshwater 



I Science, N. S., Vol. XIX, 1904, p. 503. 



" "Santa Cruz Folio," Geologic Atlas U. S., 1909. ' 



