32 
OIL DISTRICTS OF SOUTHERN CALIFORNIA. 
beds of the Sespe. In addition to these, there are numerous local 
folds and one or two faults, each of which is of almost equal import 
ance to the features first mentioned. 
Both Hopper and Piru canyons, in the lower 10 miles, have been 
developed across the structure at points where the strata are exten¬ 
sively puckered, each canyon lying a little east of the axis of a sharp 
strike flexure. The western of the two axes presents a change in 
trend from N. 65°-70° W. to N. 50°-70° E. The easterly axis shows a 
reverse change from N. 60° E. through east-west to N. 80° W. Locally 
slight departures from the general trend are to be found. For 
instance, the Modelo anticline and the syncline immediately to its 
south have a direction approximately east and west, and a number of 
minor folds between 1 mile and 2 miles in length, particularly con¬ 
spicuous on the east side of Hopper Canyon, lie diagonally to the gen¬ 
eral trend of the larger flexures. Between the individual folds of the 
several trends direct continuity has not been established, but there is 
a suggestion of this in several instances, notably in the Oat Mountain 
syncline, which apparently can be traced from Sespe Creek nearly to 
the Modelo district, and again in the Lyons anticline, which almost 
certainly passes directly from the Piru Valley to Hopper Canyon. In 
any event, the folds are unquestionably the associated crumples of 
a single affected zone that passes continuously, though with wavy 
trend, from the region of Mount San Cayetano to that of Piru Creek. 
PL III, sec. X-Z', illustrates the general occurrence of petroleum in 
the mountains north of the Santa Clara Valley. The section without 
being continuous nevertheless represents in nearly their true succes¬ 
sion the formations that occupy this great area and portrays the 
structural features that prevail in most of the productive oil territories. 
The line of the section is laid down on the map (PI. I). Besides being 
somewhat irregular it presents two important offsets that were nec¬ 
essary to the generalization of the conditions. One of these offsets 
(x'-y) occurs at Little Sespe Creek and is a mile in length; the other 
(y'-z) embraces the interval between Brush Mountain and Piru Peak, 
a distance of 5 miles. In both intervals, however, the break in the 
stratigraphic succession is reduced to a minimum. 
The formations involved include the Topatopaformation; the Sespe 
formation, with its three divisions—base, middle, and top; the Vaque- 
ros formation, with its several bands of varicolored clays; the 
Modelo sandstones and their accompanying shales, a portion of which 
at least may correspond to the Monterey, and the Fernando forma¬ 
tion, which probably extends from the Miocene through the Pliocene 
and well up into the Pleistocene. Their distribution over the line of 
the section may be gathered from the illustration. There are, how¬ 
ever, certain features which it may be well to consider somewhat at 
