SANTA CLARA VALLEY : STRUCTURE. 
35 
this fold. They have produced some oil, but have not been operated 
with the same care as the wells of the Modelo Oil Company, and as a 
consequence much water occurs with the oil. 
The Nigger anticline lies a mile and a quarter south of the Modelo 
fold, being separated from it by a syncline and the fault already 
described. The strata involved are the upper Modelo sandstone and 
the shales above and below. The productive wells on this anticline 
are in the easterly tributary of Nigger Canyon, a little south of the axis 
of the fold. They are 500 or 600 feet deep, the oil having b sen encoun¬ 
tered at depths of 65 to 400 feet. 
Half a mile south of the Nigger anticline is a sharp change in the 
rocks which represents the contact between the Modelo and the Fer¬ 
nando formations. The younger beds have a northerly dip, which 
represents either an overturn at the plane of unconformity or a fault— 
perhaps both. That an unconformity exists between the Fernando 
formation and the underlying beds is beyond doubt, and many strata 
are brought successively into contact on either side of the plane. From 
the point of the ridge separating Nigger Canyon from Piru Creek east¬ 
ward for several miles beyond this stream there is a marked line of 
disturbance. A synclinal structure has been suspected, but careful 
examination indicates that this supposition may have been induced 
by the deceptive relations of the dips; in reality there is probably an 
anticline, with a very steeply inclined southern limb, which west of 
Piru Creek has possibly been the locus of a fault. At this point in the 
section, therefore, there may be a fault in proximity to a line of uncon¬ 
formity, much after the order of the unconformity and fault passing 
along the southern border of the Puente Hills from the region of the 
Santa Fe wells westward to Whittier. (Seep. 111.) Doubtless the 
dip of the Fernando strata changes from northerly to southerly 
beneath the valley of the Santa Clara, but exposures along the bottom 
lands are wanting, and the relation of the formations north of the 
river to those south of it can only be conjectured. 
REGION SOUTH OF THE SANTA CLARA. 
The mountains bordering the Santa Clara Valley on the south 
represent the west end of one of the most important uplifts of southern 
California. The center of uplift, the San Gabriel Range, consists of 
granites and related rocks. Encircling these on the west are sedi¬ 
mentary beds of Tertiary age, which constitute, in the order named 
from east to west, the lower elevations of the Santa Susana Moun¬ 
tains, Oak Ridge, and South Mountain. The structure of this sys¬ 
tem of ridges is anticlinal and notwithstanding a degree of continuity 
between the formations north and south of the upper portion of the 
Santa Clara Valley the mountains south of the river preserve, on the 
whole, remarkable independence of structure. In the western half of 
