TERTIARY FAUNAS OF THE. PACIFIC COAST 525 
folding and faulting were intense, the greatest disturbances accom- 
panying the uplift of the mountain ranges to an altitude of thousands 
of feet. In other regions low broad folds were formed during the 
post-Monterey disturbance, and the strata were not upheaved to a 
great altitude. Faulting on a most magnificent scale took place along 
the earthquake rift and certain other fault-zones, especially that in the 
Salinas Valley, and along these lines of displacement, masses of 
granitic rocks, which during the preceding epoch had been subject 
to little or no erosion, were suddenly thrust upward and left exposed 
to the ravages of streams that assumed the proportions of torrents in 
certain regions, as for instance adjacent to the Carrizo Plain in south- 
central California. ‘The post-Monterey disatrophic movements in 
the Puget Sound province also produced sharp relief as is evidenced 
by the coarse sediments deposited immediately following the disturb- 
ance. The localization of movement during the period is exemplified 
at numerous localities in the Coast Ranges. 
Throughout much of the coastal belt, and probably likewise in 
the interior, great volcanic activity took place during the middle 
Miocene, this being the last epoch of volcanism in the Coast Ranges 
south of San Francisco. During this post-Monterey period of 
“diastrophism general subsidence took place over most of the areas 
which were under water during the lower Miocene, and, in addition, 
extended northward from San Francisco Bay into the Sacramento 
Valley and along the coast to the California-Oregon line and south- 
ward down the Willamette Valley of Oregon. A new channel was 
apparently opened across the northwestern end of the Olympic 
Peninsula, and the Colorado Desert country of southern California 
and Arizona which for a very long time had presumably been free 
from marine conditions was occupied by an arm of the sea. 
THE UPPER MIOCENE PERIOD 
DISTRIBUTION AND CONDITIONS OF DEPOSITION 
With the possible exception of that in the Eocene the subsidence 
immediately preceding and extending into the upper Miocene was 
the most important in the Tertiary history of the Pacific Coast. As 
a result, the formations of this epoch occupy a very considerable 
percentage of the surface of the present land-area. The sediments 
