PUENTE HILLS : BREA CANYON FIELD. 
121 
being particularly persistent. Midway between the base and sum¬ 
mit of the hill there is a calcareous pebbly layer, which is also fossil- 
iferous, yielding a lower Pliocene fauna. The beds forming the 
lower slope north of the stream, although perhaps not a repetition 
of the beds south of the canyon, are unquestionably of the same 
formation. 
A small body of limestone a few feet across, together with a little 
shale similar to the Puente material, was observed in the Fernando 
of Brea Ridge. A similar occurrence was noted near the Union 
wells in the La Habra district. Both are unusual and inexplicable. 
Opposite the entrance to Brea Canyon the Fernando formation is 
succeeded on the north by shale, thin-bedded sandstone, and cal¬ 
careous concretions characteristic of the lower divison of the Puente 
in this region. A narrow dike of diabase extending in an east-west 
direction for nearly a mile intrudes these Puente beds a short dis¬ 
tance north of Brea Canyon. The shale and sandstone are directly 
traceable into those which occupy the heart of the general anticline 
2 miles to the west, in the region of the Puente Oil Company’s wells. 
They are overlain by the Puente sandstone in the eastern half of 
this field, and at the divide between Brea Canyon and the drain¬ 
age of the Olinda field the upper shale in turn appears, in contact 
with the Fernando. In the western half of the field the sandstone 
and the overlying shale are wanting, having been carried beneath 
the surface, possibly by the Puente fault, which may here pass along 
the northern slope of the canyon. Notwithstanding, however, the 
evidences of faulting in the severe crushing which the strata have 
undergone, it is also possible that the unconformity admittedly 
existing between the Fernando and the older formations may prove 
to be accountable for the variation in the succession of strata, the 
younger members of the earlier formation having been uplifted and 
removed prior to the deposition of the later conglomerate and asso¬ 
ciated sediments. East of the east fork of Brea Canyon the Puente 
sandstone regains its prominence, and from this locality almost to 
the valley of the Santa Ana and the lowlands about Chino it is the 
most conspicuous formation of the hills. 
STRUCTURE. 
The structure about lower Brea Canyon is difficult to read, but 
from what has already been said the inference may be drawn that 
it is probably in direct general continuation with that both to the 
east and west; that is, the sharp folds, faults, and unconformity 
existing in the hills of the Santa Fe region extend along the north¬ 
ern slopes of the canyon, passing thence across the spur immediately 
west of its mouth to the edge of the prairie opposite the Puente oil 
