100 
SANTA MARIA OIL DISTRICT, CALIFORNIA. 
beds underlying the area is a northwestward-plunging anticline which 
is here called the “Hartnell. ” There is both surface and underground 
evidence of its presence, hut its exact location is, of course, only con¬ 
jectural. As will be noticed on examining the map (FI. X, p. 92) 
the northern flank of the anticline is much steeper than the south¬ 
western, this fact apparently having a direct hearing on the produc¬ 
tiveness of the wells penetrating this flank. 
GEOLOGY OF THE WELLS. 
The surface distribution of the formations in the immediate vicinity 
of the little swale on the ridge in which Brookshire wells Nos. 3 and 4 
are situated is very interesting. The bottom of the swale is Monterey 
(Miocene) shale; unconformably overlying this on the south is fossil- 
iferous Fernando (Pliocene) sandstone and conglomerate; immedi¬ 
ately north of the swale is terrace-deposit (Pleistocene) sandstone. 
(See PI. XI, B.) It has been suggested that such a condition is most 
easily explained by the presence of a fault through the swale, the 
downthrow being on the north. The logs of the wells in the immediate 
vicinity, however, offer evidence that such is not the case, but that 
the underlying Monterey strata, followed almost immediately north 
of the swale by fossiliferous Fernando beds, plunge steeply north¬ 
ward and are overlain unconformably by the low-dipping or prac¬ 
tically horizontal terrace beds which are exposed on the ridge north 
of the swale. Some of the wells starting in the post-Monterey forma¬ 
tions penetrate sand and gravel for a distance of more than 600 feet 
before entering the Monterey. Limestone, probably corresponding 
layers associated with fossiliferous beds at the base of the 
Fernando in the railroad cut north of Schumann, is reported as occur¬ 
ring next to the Monterey shale in one of the wells. Water is encoun¬ 
tered in gravel at various horizons in the Fernando between the depths 
of 150 and 600 feet. Hartnell well No. 3 and Brookshire well No. 1 
(the latter about half a mile northeast of the area under discussion), 
which penetrate the water-bearing Fernando, are used as water wells. 
From the base of the Fernando to their bottoms the wells penetrate 
blue and brown shale, and very rarely fine sandy layers. “Shell’’ 
strata, many of them underlain by gas and some by oil and gas, are 
encountered here and there throughout the shale. 
The first oil zone (A) occurs about 400 feet above zone B, is struck 
at depths ranging from 2,150 to more than 3,000 feet, and is said to 
be from 2 to 5 feet thick. On examination of the material coming; 
from this and the underlying productive zones, it is quite apparent 
that the oil must come from the joint cracks or interstices between 
the fragments of more or less fractured shale, as no true sands of suffi¬ 
cient coarseness to allow the rapid transmission of the oil have been 
encountered in the productive zones in the wells of this group. 
to the limy 
