i kldeidge] ASPHALT AND BITUMINOUS ROCK DEPOSITS. 303 
in the range bordering the Salinas Valley on the east. These sand- 
stones are locally heavily impregnated with bitumen, and near Santa 
Cruz are extensively quarried for paving purposes in San Francisco 
and elsewhere. 
The Monterey formation is of particular importance, in that for 
almost the entire length of the State its terrane is more or less con- 
spicuously marked with petroleum or maltha seepages, while its sandy 
members may appear as minor storage reservoirs of oil, these now 
altered at the outcrop to a material of pasty consistency, which forms 
with the sand grains an asphaltic compound of considerable richness. 
| Such sandy beds occur at Point Arena, in the San Antonio Valley, 
and in the region of the Sisquoc. The shales of the Monterey are not 
only generally bituminous, but some of their more arenaceous and 
porous members are also especially rich, doubtless having received 
an inflow of petroleum from their adjoining and less open associates. 
It is in the shales of the Monterey, too, as well as in the Middle Neo- 
cene, that veins of the more solid bitumens, mixed with elastic mate- 
rial derived from the country rock, are found. Except for the clastic 
material, the bitumen would resemble in structure the asphaltites, 
though still differing from them in other features. Veins of this 
description are conspicuous in the vicinity of Santa Maria, Santa 
Barbara, and Asphalto. Near the latter place the asphaltic material 
is intimately related to, even associated with, petroleum. 
The San Pablo formation, at least that portion of it in the San Luis 
Range, has been converted into a vast storage reservoir. It is the 
surface terrane over an area of nearly 50 square miles a short dis- 
tance southwest of San Luis Obispo, and perhaps half its outcrop here 
shows impregnation with bitumen in greater or less degree, locally 
to a high degree. In the same region scattered bodies of the Paso 
Robles formation have also been infiltrated where resting on the San 
Pablo or the Monterey. 
The San Pablo is also, perhaps, represented in the region of the 
Sisquoc, 40 miles southeast of Santa Maria, where along the southern 
base of the San Rafael Range is a highly enriched body of sandstone, 
of doubtful correlation from its structural association with recognized 
Monterey sandstones, but possibty of the age suggested. It is locally 
one of the richest sandstones in California. 
In the region of La Graciosa Hills, to 10 miles south of Santa 
Maria, there rests upon the Monterey, unconformably, a heavy body 
of loosely coherent sands or sandstone commonly regarded as Plio- 
cene. Cracks have developed in the formation, and have been 
filled with bitumen carrying from 30 to 60 per cent of clastic matter. 
The material resembles in general appearance that already referred 
to as of vein form in the Middle Neocene near Asphalto. Here, 
again, it has been found in association with petroleum. 
Post-Pliocene sandstones are found with small gash veins and 
