10 REPORT OF THE CALIFORNIA EARTHQUAKE COMMISSION. 
shale with five formations of sandstone, the latter being at the bottom and top of the 
series. The series is known as the Monterey series, and its various members have dis- 
tinctive formational names. While the oscillation of the coast so clearly recorded in the 
strata near the Bay of San Francisco is not apparent in the southern Coast Ranges, it is 
by no means certain that they were not affected in a similar way. The vertical move- 
ment involved was not great, and such a movement might have extended over the deeper 
portions of the area of deposition in Monterey time without effecting a sufficient change 
in the depth of the water to alter the character of the sediments. The Monterey sea 
apparently did not, even at the time of its maximum transgression, extend far over 
the region of the northern Coast Ranges, and a line drawn from Tehachapi to Cape 
Mendocino would probably represent the general position of the shore at the close of 
Monterey time. 
At the close of the Miocene, the Coast Range region was disturbed by orogenic move- 
ments and uplifted into the zone of erosion. It was then deprest irregularly so as to 
give rise to local basins of sedimentation in which accumulated great thicknesses of Plio- 
cene beds, particularly about the Bay of San Francisco and southward. The oldest of 
these Pliocene formations is the San Pablo, which lies unconformably upon the Monterey 
strata. This is essentially a sandstone formation with a thickness of from 1,000 to 2,000 
feet. It occurs on both sides of the Coast Ranges from the vicinity of the Bay of San 
Francisco southward and appears to have been laid down in two basins, separated by a 
barrier corresponding to the general axis of the present Coast Ranges. The formation 
on the east side of the range is characterized by a notable admixture of dark andesitic 
ash, which gives the unweathered exposures of the sandstones a distinctly blue color. 
This formation has a fauna of over 100 species, of which more than 40 per cent are living 
forms. This fact, and the unconformable superposition of the formation upon the 
Monterey, are warrant for placing it in the Pliocene. On the west side of the Coast 
Ranges, the San Pablo is best known in San Luis Obispo and Santa Barbara Counties, 
and is there free from volcanic admixtures, tho the basal beds are very commonly charac- 
terized by the presence of asphaltum, which cements the sand together and constitutes 
the well-known bituminous rock of the region. This asphaltum appears to have originated 
in part as a seepage from the upturned bituminous shale of the Monterey along the shores 
of the San Pablo sea, and molluscan remains of San ,Pablo age are often embedded in it. 
Succeeding the San Pablo, but nowhere, so far as the writer is aware, reposing directly 
upon it, is the Merced series. The sediments composing this series were laid down in 
rather acute geosynclinal troughs, resulting from orogenic deformation of the coast in 
middle Pliocene time. Three of these troughs are known. The most northerly is that 
now occupied by the Valley of the lower Kel River in Humboldt County; the second is 
largely occupied by the Santa Rosa Valley in Sonoma County; the third is on the Penin- 
sula of San Francisco, extending thence south to the coast of Santa Cruz County. The 
Merced strata in the Valley of the lower Eel River, and the typical Merced section near 
San Francisco, show each a thickness of something over a mile. In Sonoma County the 
marine Merced beds grade eastward into fluviatile conglomerates, admixed with volcanic 
ashes. The maximum thickness is about 3,500 feet. The lower part of the series is here 
characterized by a considerable volume of white voleanic pumiceous tuffs, which thin- 
out rapidly to the westward. These were in part laid down directly on a land surface, 
burying forests of huge sequoia, whole trees being now completely silicified.*_ On the 
coast of Santa Cruz County, the series is represented by strata of lower stratigraphic 
horizons than nearer San Francisco, these lower beds having been called the Purissima 
formation, altho the sedimentation was continuous with that of the Merced. The 


‘ Fora description of the Merced beds of Sonoma County and the underlying pumiceous tuff, a paper 
by V. C. Osmont, Bull. Dept. Geol., Univ. Cal., vol. 4, No. 3, should be consulted. 
