INTRODUCTION. 
13 
divisible into two distinct parts—the upper, the bituminous shales, and the lower, 
the gypsiferous clays. Below the clays are sandstone, shales, and conglomerates 
resting on the gabbro and serpentine. * * * The strata of volcanic ash appear in 
the lower Miocene beds. There are three distinct horizons, the lowest resting on the 
gabbro. 
The igneous rocks are treated in especial detail in this paper and 
a very good description is given of the bituminous shales. The con¬ 
clusions of the present writers are in agreement with the statements 
above quoted and the others contained in Fairbanks’s paper. 
In 1901 George H. Eldridge gave an admirable general outline 
of the topography and geology of the country surrounding the 
Santa Maria field in his treatise on “The asphalt and bituminous- 
rock deposits of the United States,” and discussed in detail its asphalt 
deposits. 0 He says: 
The geology of the region embraces an underlying series of folded Monterey shale 
of both the soft and more organic material and that which is hard and siliceous, but 
the former predominates. So far as observed by the writer this series of beds was 
not exposed at any point in its entirety. Overlying the Monterey unconformably, 
and especially developed in La Graciosa Hills, is the heavy and extensive deposit of 
Pliocene sands, grits, and conglomerate already referred to. The composition of the 
later deposit is chiefly quartzose. 
Eldridge “ observed a prevailing central fold somewhat to the north 
of the topographic axis of the ridge” south of Waldorf, in the Cas- 
malia Hills, this being no doubt the fold described in the present report 
as the Schumann anticline. He says further: 
The Pliocene * * * shows a less degree of folding than the underlying Mon¬ 
terey, yet the movement that produced the pre-Pliocene ridge has apparently been 
continued subsequent to the deposition of the materials of this age, for gentle dips 
of from 2° to 10° are to be observed in the later formation. 
In discussing the country east of Los Alamos, between the San 
Rafael Range and the Santa Ynez Valley, which he calls the Los 
Alamos region, Eldridge says: 
In structure the Los Alamos region presents a series of folds which are in general 
coincident with the topographic ridges and valleys. * * * It is worthy of note that 
the valleys of the region under consideration for the most part occupy the synclinal 
troughs. It is possible that some of them also occupy fault lines. * * * The gen¬ 
eral trend of the folds for the Los Alamos district, and indeed for a great stretch of coun¬ 
try beyond, is N. 70° to 80° W., the dips being north and south. Excepting in their 
trend, however, there is but little regularity in the disposition of the folds, and their 
axes, both longitudinal and transverse, vary greatly in length. In addition to the 
main and conspicuous folding that has been described, there are frequent crumples 
of minor importance. 
In another place Eldridge mentions a lens of limestone included 
in the serpentine in a high bluff just north of Alamo Pintado Creek, 
alomr the old beach line where the Fernando was deposited upon the 
Franciscan at the base of the San Rafael Mountains. This lime- 
a Twenty-second Ann. Rept. U. S. Geol. Survey, pt. 1, 1901, pp. 424-441. 
1784—Bull. 322—07-2 
