64 
SANTA MARIA OIL DISTRICT, CALIFORNIA. 
hills was probably at least partly covered during the uplift of the 
coast by marine terrace deposits similar to those found elsewhere in 
the region, these being later buried by the gathering wind-blown 
sand. Recent marine shells are widely scattered over the surface 
of this sand, but are not considered by the writers as indicating its 
marine origin. They were probably carried there by Indians or 
birds. 
South of the Casmalia Hills, where the coast is open to the 
winds, sand dunes are continually forming and covering up the ter¬ 
race deposits. The sand is not retarded by an inland barrier, how¬ 
ever, as on the north of the hills, and no such vast deposit has been 
formed. The sand is continually being carried into the interior 
valleys and spread thinly over a wide area. 
ALLUVIUM. 
All the valleys of this region contain a certain amount of alluvial 
material and stream gravels, which reach in many localities a thick¬ 
ness of 50 feet or more. In some places the deposit is earthy, in 
others sandy earth, and in still others pure sand, gravel, or clay. 
It is as a rule horizontally stratified. Recent deposits of this charac¬ 
ter attain considerable extent in the wide valleys, but it is not easy 
to distinguish them from Quaternary deposits of different age or of 
somewhat different origin. They are mapped as distinct only in the 
larger valleys and the contact lines are arbitrary. Practically all 
the hills and valleys within the territory mapped have a covering 
of soil. 
IGNEOUS ROCKS. 
GENERAL STATEMENT. 
The formations in this region are chiefly of sedimentary origin 
but eruptive and intrusive igneous rocks of various ages appear. 
These are all basic in composition. Layers of volcanic ash high in 
silica interbedded with the Monterey are discussed with the sedi¬ 
mentary series (p. 37). The center for igneous rocks is in the region 
around Point Sal of which Fairbanks made a special study, and 
the statements here made in regard to the igneous rocks of that region 
are based largely on his description.® 
IGNEOUS ROCKS OF PRE-MONTEREY AGE. 
Fairbanks describes a small intrusion of basalt having a laccolithic 
appearance in the Knoxville (lower Cretaceous) shales north of 
Mount Lospe, in the Casmalia Hills, and a large neighboring area 
of spheroidal basalt that he is certain is older than the Monterey 
a Fairbanks, H. W., The geology of Point Sal: Bull. Dept. Geology, Univ. California, vol. 3, 1896, 
pp. 1-92, 
