26 SANTA MARIA OIL DISTRICT, CALIFORNIA. 
the long dry season almost complete evaporation of surface moisture 
takes place, and there is little erosion through the aid of water. 
Throughout the latter part of the Quaternary period the rate of ero¬ 
sion has probably been slow. 
CLIMATE AND VEGETATION. 
The climate of this area is that of the coastal region of California. 
It is equable the whole year round, excessive heat or cold being 
very rare. The days are mild, the nights chilly. The region is sub¬ 
ject to the inroads of heavy fogs and driving winds from the open 
ocean, but this is true to a lesser degree in the eastern angle of the 
basin, where there are protecting hills on all sides. The winds 
blow very strongly from the west and northwest up the radiating 
valleys that open to the coast. The region is subject to earth¬ 
quakes, some of which would seem to be of local origin. 
The vegetation in the northern part of Santa Barbara County is 
open, as in the neighboring portions of California. There are almost 
no dense groves of trees, most of the hills being sparsely clothed 
with a scattering growth of small trees, usually live and white oaks, 
and bushes, or else entirely bare, except for sagebrush and grass. 
The wide terraces and hills of soft sand are commonlv overgrown 
with so-called tarweed and are otherwise almost bare. In the val¬ 
leys near the coast grow many willows; in the more protected val¬ 
leys farther inland thrive large sycamores, cottonwoods, and live 
and white oaks. The steep slopes of the San Rafael Range are 
sparsely set with small oaks, pines, and yuccas, and, like those of 
the Santa Ynez Range, are covered in parts by dense thickets of 
undergrowth. 
The vegetation of the hill ranges of the basin region is typically 
illustrated by PI. IX (p. 80) and of the San Rafael Mountain region 
by PI. VI (p. 46). 
GEOLOGY. 
SEDIMENTARY FORMATIONS. 
GENERAL STATEMENT. 
The formations involved in the geology of this district (see PI. II) 
include the Franciscan (Jurassic?); Knoxville (lower Cretaceous); 
pre-Monterey rocks (which may include both Cretaceous and older 
Tertiary); Tejon, Sespe, and Vaqueros, undifferentiated (Eocene- 
Miocene); Monterey (middle Miocene); Fernando (Miocene-Pliocene- 
Pleistocene); and Quaternary. The maximum known thickness of the 
Tertiary and early Quaternary formations combined is 13,200 feet. 
The following table shows the correlation of these formations with the 
