86 
OIL DISTRICTS OF SOUTHERN CALIFORNIA. 
toward the base of the series. Concretions, some of them compara¬ 
tively large and rounded, characterize certain horizons. The shale is 
for the most part earthy or sandy, but through it may be traced bands 
of harder and in some places even siliceous rock. Limestone concre¬ 
tions are also sparingly present. Both shale and sandstone have been 
more or less impregnated with petroleum, as well as with iron and 
salts of other minerals. Along the axis of the anticline, wherever 
crushing has been particularly severe, occur important seepages of 
petroleum. 
Overlying the thin-bedded sandstone and shale, with compara¬ 
tively sharp passage from the one to the other, is heavy-bedded sand¬ 
stone divided by minor layers of sandy shale. The sandstone is gray 
to yellow in color, although yellow appears to characterize more gen¬ 
erally the lower beds. The sand is coarse and locally gritty or even 
pebble bearing. Well up in the mass conglomerate appears, becoming 
in the outer ridges of the Santa Susana Mountains, a conspicuous fea¬ 
ture in the geology. The sandstone and shale in the lower 1,000 feet 
of this younger formation have been impregnated in varying degree 
with petroleum, and from some of them come seepages, indicating 
considerable richness. From one or another member of this group of 
beds is derived the oil in the producing wells of Tapo Canyon. 
Conformability appears to exist throughout the succession of strata 
above described, from the lowest, encountered in the heart of the anti¬ 
cline, to the highest, observed at the outer edge of the range. It is 
difficult, therefore, to recognize any true basis on which to segregate 
the beds into distinct formations, yet in a broad way they are separa¬ 
ble into a mass of conglomerate and associated heavy-bedded sand¬ 
stone and shale which bear a distinct resemblance to the Fernando of 
other localities in the Santa Clara district on the one hand, and thin- 
bedded sandstone and shale of a siliceous character, which closely 
resemble the banded chocolate-colored and gray shale and sandstone 
farther west in Oak Ridge and the Modelo in the range north of the 
Santa Clara on the other. For the sake of mapping, the dividing line 
has been taken at the lower horizon of the heavier conglomerate in the 
main Tapo Canyon, a quarter to half a mile above its mouth, occurring 
somewhat farther up on the streams to the east and somewhat lower 
down on those to the west. 
OIL WELLS. 
The oil wells in the territory just described comprise, in order from 
west to east, the Torrey, Eureka, and Tapo groups, each being desig¬ 
nated by the canyon in which they are drilled. 
