330 HANNIBAL: A PLIOCENE FLORA FROM CALIFORNIA 
tion, and earlier by Cooper’ as the Contra Costa, a fresh-water 
deposit of late Miocene age in the Berkeley Hills. The faunal 
evidence does not bear out such a correlation. 
CHARACTER AND DISTRIBUTION OF BEDS 
The formation consists of a well-bedded series of clays, slits, 
and sands with minor gravel strata, of wide extent, underlying 
and outcropping about the edges of the Livermore, Santa Clara, 
and San Benito valleys. A large mass fills a formerly extensive 
depression southwest of Mt. Hamilton, of which San Felipe Valley 
is a part. Remnants extend south as far as Cook P. O. in San 
Benito County, a distance of nearly a hundred miles from Liver- 
more. The occurrence of sediments about Portola, thirty miles 
west of the latter point, indicates a considerable breadth at this 
latitude. The northward extension of the former lake is uncertain, 
since the sinking of the San Francisco Bay region in comparatively 
recent times has permitted the burial of its sediments beneath 
the valley alluvium. 
The thickness of the series is not inconsiderable, but varies 
widely. In the foothills near Tres Pinos fully 1,000 feet of nearly 
horizontal strata overlie the Miocene, while the top of the series 
is cut off by erosion. A section down Calabazas Cafion in the 
Santa Cruz Mountains, without exposing the basal beds, was 
estimated to be 3,000 feet in thickness to a point where the upper 
strata are similarly absent. 
It is highly probable that the entire Santa Clara formation 
was deposited at or comparatively near sea level. The character 
of the. flora furnishes proof that the elevation could hardly have 
been greater than 1,000 feet and was probably much less. It is 
difficult to conceive that a single body of water, or quite as 
probably several connected bodies, of this extent could exist at any 
considerable elevation in proximity to the ocean continuously for 
a sufficient period of time to deposit over half a mile of sediments 
without draining the lake by stream corrosion alone. The enor- 
mous thickness of. the beds is perhaps explainable on the assum p- 
tion that the valleys acted as catchment basins with the bottoms 
sagging beneath the oad of sediments, It might be added that 
7 Proc. Calif. Acad. Sci. 4: 169. 1894. 
