18 
OIL DISTRICTS OF SOUTHERN CALIFORNIA. 
LOWER SANDSTONE. 
The lowest member, a massive, heavy-bedded sandstone, rests 
directly and apparently conformably upon the Yaqueros shale. It 
varies in thickness from 200 or 300 feet to perhaps 1,500 or 2,000 
feet. It is white to yellowish gray in color. Locally the sandstone 
is gritty, bearing also a dark-gray to black chert, and a few pebbles 
of another sandstone. It contains spherical and elliptical concre¬ 
tions from 1 foot to 5 feet in diameter, which are so prominent and 
so resistant to weathering as to form a conspicuous characteristic of 
the member, the more so because ol the utter lack of such concre¬ 
tionary bodies in a second, otherwise similar sandstone that occurs 
higher up. The upper half of the sandstone is less concretionary 
than the lower and is also thinner bedded, the layers being separated 
by shale of a dark-drab color, which carry scattered gray limestone 
concretions that weather yellow. Traces of organic life are also 
visible. This member is usually stained dark with petroleum. 
This lower sandstone early received the name Modelo, but the 
writer has thought it best to assign the name tentatively to the entire 
formation described in the opening lines of this section. The sand¬ 
stone is best displayed in the bold escarpment east of Tar Creek and 
is also heavily developed in Hopper Canyon and at the head of 
Modelo Canyon. A large number of productive wells have been 
drilled in Modelo Canyon, the oil being doubtless derived from some 
of the lower horizons of the formation. Plate II, A, gives an idea of 
the appearance of this sandstone in the region north of the Modelo 
wells. 
UPPER SANDSTONE. 
The upper sandstone of the Modelo formation is but little less con¬ 
spicuous than the lower, although its maximum thickness has been 
estimated at only 900 feet and in many places it is even less. It has 
the same mineral constitution as the lower bed, being composed of 
white, subangular quartz, with a trace of the salts of iron, which 
have colored it slightly yellowish. A considerable amount of dark 
chert is also present, and in one locality beautiful green and brown 
pebbles of siliceous shale were observed. The member is, however, 
nonconcretionary. It is also thinner bedded than the lower sand¬ 
stone and for 100 feet at the base is not only comparatively micaceous, 
but is split by minor bodies of shale, the whole somewhat darker than 
the portion overlying, seemingly from the presence of dried petroleum. 
This portion weathers a peculiar bluish gray. 
This sandstone is conspicuously developed in the region of Hopper 
Canyon, where it lies in a well-marked syncline that to the east is 
sharply compressed and, perhaps, faulted. South of this syncline the 
sandstone is involved in one or two other folds and finally, between 
Hopper and Nigger canyons, passes beneath the Santa Clara Valley. 
