528 RALPH ARNOLD 
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 Phocene 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 earher 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 
t Science, N. S., Vol. XIX, 1904, p. 503. 
2 “Santa Cruz Folio,” Geologic Atlas U. S., 1909. 
