30 OIL DISTRICTS OF SOUTHERN CALIFORNIA. 
when the general geology of the region shall be the primary object of 
investigation. The strip of enigmatical territory occupied by the 
valley therefore forms an obviously ideal line of division between the 
I two more or less structurally distinct areas north and south of it, and 
advantage will be taken of this fact to discuss each of these areas sepa¬ 
rately. 
REGION NORTH OF THE SANTA CLARA. 
Of the great mountain system north of the Santa Clara Valley the 
southern member, the Topatopa Range, is alone involved in the 
geology of the developed oil fields. This range is 30 or 40 miles long; 
its trend is east and west; its structure is anticlinal, the axis passing 
a few miles north of the area mapped in Pis. I and V. 
In the region of Sespe Creek the axis of the anticline lies beneath the 
crest of the range and is occupied by characteristic quartzites and 
slates to which has been assigned the name Topatopa formation. The 
anticline is symmetrical and is well displayed in the canyon walls. 
About the Topatopa formation bend in succession the Sespe, Vaque- 
ros, Modelo, and Fernando beds, all strongly developed and forming 
conspicuous features of the landscape. Toward the east the point of 
the anticline broadens, the Modelo sandstone outcropping in a wide 
sweep about the axis and the youngest beds covering a still greater 
area in their arch. The west end of this great anticline has not been 
located, the consideration of its east end being sufficient for the pur¬ 
poses of the present report. 
The northern side of the anticline is unexplored, and whether the 
prominent ridge of granite lying to the north is produced by faulting 
or is a part of a separate dynamic system is unknown. 
The southern limb of the anticline presents an intricate succession 
of secondary folds and accompanying faults that extend from Ventura 
River and the Ojai Valley beyond Piru Creek. East of Santa Paula 
Creek the strata are strongly bowed to the south. At Sespe Creek the 
curvature is as pronounced in the opposite direction. Immediately 
west of Hopper Canyon the convex side of the bend is again to the 
south, while east of Piru Creek regularity of trend is once more ap¬ 
proximately resumed. North and east of the Ojai Valley the south 
limb of the Topatopa anticline is overturned. 
An examination of the map makes it obvious that faults are the 
dominant structural feature in the Ojai Valley, at the west end of the 
territory under discussion. No less than five fractures cross the 
region from east to west, divergent in trend from N. 60° W. at the 
north to S. 75° W. at the south. The result has been a succession of 
interfault blocks more or less limited in size, with considerable varia¬ 
tion in the strata opposed. The faults originated nearly at a common 
center in the great fracture passing in front of San Cayetano Moun- 
