126 
OIL DISTRICTS OF SOUTHERN CALIFORNIA. 
STRUCTURE. 
The Olinda oil fields lie on the southern limb of the general anti¬ 
cline of the Puente Hills. The prevailing dip of the strata is, there¬ 
fore, to the southwest, but an opposite dip is encountered at many 
places by reason of subordinate folds developed on the flanks of the 
principal flexure. The axis of the main fold, which trends N. 65°- 
70° W., lies somewhat less than a mile north of the oil belt, those of the 
lesser folds traversing the intervening space. 
The northern edge of the oil belt, which is closely coincident with 
the base of the main body of the hills, is the locus of an extremely 
sharp fold that has many of the attendant features of a fault. In 
immediate proximity to it, also, is a trace of the contact between the 
Fernando and older formations, but whether this is a plane of fault¬ 
ing or of unconformity it is difficult to say. Perhaps the conditions 
are the combined results of the two, for the evidence for each at one 
point or another seems almost conclusive. The formations which are 
in contact are the Puente sandstone and the shales beneath and 
above on the north, and the conglomerate, sandstone, and clay of the 
Fernando formation on the south. 
The zone of disturbed strata is traceable westward directly into 
Brea Canyon and eastward across the point of the ridge between 
Soquel and Telegraph canyons well into the hills south of the latter. 
It is marked in numerous places by heavy seepages of oil, which, how¬ 
ever, appear to be from the Fernando rather than from the older 
beds. Beyond Telegraph Canyon the examination was not con¬ 
ducted in detail, but it is a significant fact that in the vicinity of 
Santa Ana Canyon, directly in the line of maximum crushing in the 
Olinda field, is another area of disturbance found by Mr. Homer 
Hamlin in a hurried inspection of the geologic conditions there 
existing. 
The evidence for a fault in the Olinda field consists in an irregular 
succession of beds, a zone of crushed strata for 200 or 300 feet on 
either side of the interformational line, sharp flexures with local down¬ 
ward curve of the Puente beds on the north of the suggested plane 
of displacement and upward bend of the Fernando on the south, 
and the high inclination of both formations. These features also 
attest to the development of the fracture subsequent to the deposi¬ 
tion of the Fernando, although prior to this period faulting might 
have taken place along a line practically coincident with the later 
displacement. In fact, there is ample proof in the hills area that 
the rocks of the Puente had been considerably folded before the Fer¬ 
nando formation was laid down upon them, and it may be that they 
were faulted as well. 
