66 
SANTA MARIA OIL DISTRICT, CALIFORNIA. 
Another intrusion of probable post-Monterey age forms a single 
outcrop in the hills 7 miles northeast of Point Conception. It is a 
dike of basic porphyry related to basalt. On one side of the outcrop 
the bases of horizontally lying rough pentagonal columns are well 
exposed. It is not known whether the sedimentary rocks through 
which this is intruded belong to the Monterey or the upper part of the 
Vaqueros. 
GEOXjOGIC history. 
EARLIEST PERIODS. 
The general geologic aspect of the Santa Maria district is that of a 
region of comparatively recent geologic formations. Tertiary rocks, 
in places covered by Pleistocene deposits, are predominant, those 
of Cretaceous and Jurassic age less widespread, and older formations 
entirely absent. The Tertiary has received almost all the attention 
in the present study and little can be said of the history of the region 
previous to that period. The much-disturbed and metamorphosed 
Jurassic sediments (Franciscan), intruded by serpentine, form the 
basement of the whole region, but outcrop only very locally. In Cre¬ 
taceous time a considerable thickness of marine sediments was laid 
down, but these deposits were probably not greatly disturbed before 
the beginning of deposition in the Tertiary. To the present time they 
have remained unmetamorphosed and no more affected by moun¬ 
tain-making forces than later formations. Igneous intrusions, how¬ 
ever, took place at different times in the Cretaceous. 
EOCENE PERIOD. 
All the greater divisions of the Tertiary, with the possible excep¬ 
tion of the Oligocene, are represented by marine sediments, the 
major part of this time having been taken up by sedimentation. 
The relations between the Cretaceous and Eocene rocks have not 
been studied. Sedimentation began at some time in the Eocene 
not yet determined, in the southern portion of the region mapped, 
and continued nearly to the end of the Eocene, when it ceased for a 
period of unknown length. It was probably in the period just pre¬ 
ceding that of the deposition of the Eocene sediments that the forces 
began to work which caused the structural features south of the 
region where the San Rafael Mountains now stand to assume an east- 
west trend. In this way may have been formed the depression 
extending east and west across the region now occupied by the 
Coast Ranges, which afforded a basin of deposition for the Eocene 
and possibly a connection between the ocean and the basins in which 
strata of the same age were deposited in the interior. A large part 
of the Santa Ynez Mountains is composed of Eocene strata which 
have been lifted up along east-west lines of structure. The main 
