SANTA CLARA VALLEY : TOPATOPA FORMATION. 5 
and which probably represent all of the Pliocene and overlap into 
both the Miocene and the Pleistocene; the Modelo formation, of sand¬ 
stones and shales, which may prove to be the homologue of the 
Monterey; the Vaqueros formation, of shales, interbedded limestones, 
and sandstones; the Sespe formation, in the main a great body of 
brownish-red sandstones and conglomerates; the Topatopa forma¬ 
tion, of quartzites, sandstones, and hard, more or less siliceous, and 
earthy shales; and an older basement of gneisses and granites, prob¬ 
ably of Jurassic age. This series of formations appears to be con¬ 
formable from the base of the Topatopa as far up as the base of the 
Fernando, where a distinct chronologic break is observable. The 
later Pleistocene, also, is unconformable with the beds below, resting 
here upon one formation, there upon another. 
GRANITIC BASEMENT. 
GENERAL CHARACTER AND DISTRIBUTION. 
The oldest rocks in the territory under discussion are the gneisses 
and granites which underlie the Tertiary sediments east of Newhall. 
The gneisses are close grained, micaceous, conspicuously banded, and 
greatly contorted. In the region mentioned they strike approximately 
N. 70° W. and dip 50°-80° N. The underlying granitic rocks are mostly 
medium to fine-grained diorites, similar to those lying farther east 
which make up a large part of the San Gabriel Range. These and the 
other crystalline rocks found in the San Gabriels have been described 
by Arnold and Strong.® The granitic rocks are probably contempora¬ 
neous with those of the Sierra Nevada, which are of late Jurassic age. 
The most remarkable thing in connection with the gneisses east of 
Newhall is the occurrence in them of a very light oil, approaching a 
naphtha. Alternative hypotheses regarding the origin of this oil are 
given in the discussion of the geology of the Elsmere field (pp. 100-101). 
TOPATOPA FORMATION. 
GENERAL CHARACTER. 
The Topatopa formation receives its designation from the name of 
the range of which it is the chief constituent. It is the lowest forma¬ 
tion outcropping in the mountains north of the Santa Clara Valley. 
Its total thickness is unknown, but about 5,500 feet are exposed. 
This consists of excessively hard, submassive sandstones and quartz¬ 
ites, the latter of a greenish-gray color, clear or mottled with white, 
and shales, which differ from the quartzites in carrying an additional 
content of mica, in the fineness of their material, and consequently in 
a Arnold, Ralph, and Strong, A.M., Some crystalline rocks of the San Gabriel Mountains, California: 
Bull. Geol. Soc. America, vol. 16, 1905, pp. 183-204. 
Bull. 309-07-2 
