GEOLOGY OF THE COAST SYSTEM OF MOUNTAINS. 21 
facilitated by the deformation of the region. The offsetting consideration to this objec- 
tion, based on the less mature aspect of this part of the valley, is that it traverses much 
harder rocks than are found in the wider valley above. Ina word, the view that the lower 
transverse stretch of Russian River may be the remnant of an original consequent stream, 
from which, by subsequent development, has been evolved the longitudinal Russian River 
Valley, has not yet been satisfactorily negatived. 
Somewhat similar features occur on the east side of the Coast Ranges. Cache Creek 
and Putah Creek, draining longitudinal valleys within the Coast Ranges, both emerge 
upon the Great Valley thru transverse gorges in the Blue Ridge, the most easterly of the 
Coast Ranges. These transverse gorges can scarcely be regarded as other than conse- 
quent trunks crossing a hard barrier within which, in softer formations, longitudinal or 
subsequent valleys have been evolved. The apparent absence of the transverse connect- 
ing links between Napa, Sonoma, and Petaluma Valleys is explained when it is recalled 
that while the streams draining these valleys flow directly to salt water, they neverthe- 
less flow to a drowned valley. The trunk stream trench from which Petaluma, Sonoma, 
and Napa Creeks are subsequent branches lies below the waters of San Pablo Bay. In 
general, Santa Rosa Valley (lower part of Russian River Valley), Petaluma Valley, 
Sonoma Valley, and Napa Valley have been evolved by erosion along synclinal axes. 
This fact also tends to weaken their interpretation as due to subsequent development by 
headwater erosion; since, if the synclinal folds were exprest as troughs at the surface 
at the time of the folding, then the drainage would have been both consequent and 
parallel to the structure. 
Coming farther south, the valley of the Bay of San Francisco and its extension in the 
Santa Clara Valley is a large feature in which deformation and erosion have probably 
played equal réles. Its trend is strictly determined by the Haywards fault line pre- 
viously described. Southward from Hollister, the valley loses its breadth and passes 
into the much more constricted valley of the San Benito River, draining the Coast Ranges 
to the east of the Gavilan Range. The Bay itself and its inland extensions afford a 
magnificent illustration of a drowned valley-land due to subsidence of the valley-bottoms 
below sea-level. 
Livermore Valley, a few miles to the east of the Bay of San Francisco and separated 
from it by the ridge of the Berkeley Hills, is a very noteworthy feature. It is a broadly 
expansive alluviated valley, bounded on the west by the degraded fault-scarp which 
limits the Berkeley Hills to the east; on the east by the slopes of Mount Diablo; and on 
the south by the slopes of Mount Hamilton. On the north it is open by way of the wide 
and low San Ramon Valley to Suisun Bay, and the northern portion of the valley 
drains this way. The greater part of the waters which come to it from Mount Diablo 
and from Mount Hamilton, however, are carried off by Alameda Creek thru Niles 
Canyon, a narrow gorge which transects the bold ridge separating it from the Bay 
of San Francisco. Alameda Creek has a hydrographic basin of 600 square miles, 
and it is a remarkable fact that it finds its outlet across the strike of the range thru 
a bold ridge, instead of following the wide open valley leading directly to Suisun Bay 
with no barrier in its path. It is a fair inference that Livermore Valley is structural 
rather than erosional in its origin and that, anterior to the acute deformation of the 
region, the drainage was consequent in the path followed by Niles Canyon. The 
deformation involved the uplift of the Berkeley Hills and the complementary depres- 
sion of the Livermore Valley tract, and this deformation proceeded at a rate which was 
sufficiently slow to permit the stream, by downward corrasion across the rising mass, 
to maintain its course. Alameda Creek in Niles Canyon is thus a remnant of the 
consequent drainage of the region and is antecedent to the uplift which gave rise to the 
Berkeley Hills. 
