332 HANNIBAL: A PLIOCENE FLORA FROM CALIFORNIA 
GEOLOGIC RELATIONS 
The youngest formation antedating the Santa Clara is the 
Purisima, a marine deposit, older Pliocene in age. The Purisima 
is confined chiefly to the ocean front, but an embayment extended 
from Half Moon Bay and Pescadero across the Santa Cruz Moun- 
tains past La Honda and Portola to the hills near Stanford Uni- 
versity and the mouth of Stevens Cafion, while another arm 
extended inland from Santa Cruz to the vicinity of Chittenden. 
The relation of the Santa Clara to the underlying Purisima 
formation, along the flanks of the Santa Cruz Mountains is prob- 
ably one of decided unconformity, though the incoherence of the 
beds has prevented its actual observation. The tilting of the 
Purisima, which is apparently somewhat greater than that of the 
Santa Clara, and the differences in distribution of the two indi- 
cate that important structural movements took place in the inter- 
val previous to the opening of the Santa Clara period. 
The older Pliocene through the Coast Ranges appears to have 
been a period of peneplanation. The movements which preceded 
the Santa Clara epoch developed the general outlines of the present 
topographic features. The relief of the mountain ranges was, 
however, far more gentle than at present, and the elevations of the 
mountains themselves decidedly less. 
Since the deposition of the Santa Clara, several important — 
geologic events have taken place in the history of the Coast 
Ranges.” Following the Santa Clara sedimentation, apparently 
without the intervention of any other deposits, the entire Coast 
Ranges were lifted more or less bodily, carrying the old lake level 
to an elevation of perhaps 4,500 feet above the sea. Rapid erosion 
ensued and the soft lacustrine beds were cut into deeply, far below 
the present valley floors. This period of intense elevation and ero- 
sion called the Sierran epoch, was widespread in California. It is 
regarded as marking the opening of the Quaternary, corresponding 
at least in part to the Glacial epoch of elevated or more northern 
regions. Subsequently a period of depression ensued, succeeded 
by temporary oscillations, which have continued to the present. 
The beds of the Santa Clara formation in the San Benito Valley 
Lawson, A.C. Bull. Dept. Geol. Univ. Calif. 1: 115, 242. 1893. Smith, J.P. 
Science IT. 30: 346. 1909. 
