52 
OIL DISTRICTS OF SOUTHERN CALIFORNIA. 
there are numerous local folds of but little less importance than those 
just mentioned. One or two of these local flexures are accompanied 
by faults, forming highly-crumpled zones. 
The portion of Sespe Canyon lying above its confluence with Little 
Sespe Creek is the seat of marked disturbance. Apparently, there 
has been not only folding in conformity with the general east-west 
trend of the main anticline, but also a transverse buckling of the strata 
along strike lines that probably took place synchronously with the 
development of the principal folds. This buckling resulted in the sharp 
changes observed in the direction of structural lines and rendered 
still more complex the general folds and faults that affect the strata, 
especially in the angle between the main Sespe Creek and its tribu¬ 
tary, Little Sespe Creek, and about the mouth of Sespe Canyon. In 
this region the regularity of the folds described in the preceding para¬ 
graphs has been almost completely destroyed, and the real structure 
is determined with difficulty. 
The valley of Sespe Creek below the canyon is filled with Pleistocene 
deposits that conceal the older formations. East of the stream, in the 
lower slopes of Oat Mountain, there is a suggestion of the structure 
in the presence of Os^a-bearing, rusty sandstone and shale, more or 
less calcareous, that closely resemble the rusty beds at the summit 
of the Sespe formation. These beds have a general N. 15° W. strike 
and an easterly dip. The strike becomes northwesterly toward the 
north, the beds evidently crossing the creek and uniting with those 
in the much-crumpled area immediately within the canyon mouth. 
To the south the rusty beds disappear beneath the overlying members 
of the Vaqueros formation, affording indications of a southerly dip 
beneath the valley. It is possible, however, that at this point there 
is a fault which has carried down the Modelo shale, bringing it into 
contact with the lower members of the Yaqueros formation and, per¬ 
haps, even with the rusty upper beds of the Sespe. 
The strikes and dips here described suggest the east end of an anti¬ 
cline, most of which lies buried beneath the recent deposits of the Sespe 
and Santa Clara valleys. It is possible, too, that the trace of an anti¬ 
clinal axis in the southern escarpment of San Cayetano Mountain, 
already referred to, may be a portion of the same flexure. In this 
case the San Cayetano fault may merge into this anticline on the east 
or it may die out in the much smaller fracture at the south end of Sespe 
Canyon, suggested in the preceding paragraph. 
In the development of the earlier geologic features in the vicinity 
of the present Sespe Canyon there appears to have been formed, at the 
close of the Miocene, a structural bay, which was later filled with 
Pleistocene and, perhaps, Pliocene sediments. The uppermost Fer¬ 
nando or Pleistocene deposits are those which to-day are exposed in 
