56 
GEOLOGY. 
The following section, representing a thickness of not over five hundred feet, will serve to 
indicate the relative positions and dip of the strata: 
SECTION NEAR THE PASS OF SAN FRANCISQUITO. 
d C b a 
a. Stratum, containing large angular blocks of red and lilac-colored volcanic rocks—trachytes and porphyries. 
b. Six to ten feet thick, compact rock, of a Vermillion red color. 
c. Breccia of small fragments of porphyry, serpentine, and a jaspery rock, imbedded in a white paste or matrix. Thin 
seams of opalescent quartz traverse this bed. 
d. A rude mixture of large, well rounded, and evidently water-worn boulders of trap rock, porphyry, trachyte, and other 
volcanic rocks, of various shades of color and variety of texture. 
e. Thin layer of angular fragments of obsidian, eight to ten inches thick. 
The strata between the conglomerate and breccia and the layer of obsidian consist of nearly 
white, fine-grained sandstone, the strata of which were not, however, fully exposed to view. 
The layer of obsidian formed a distinct dark stripe along the base of the series, and was slightly 
broken and faulted in several places. 
This was a remarkably interesting and singular accummulation of volcanic material or debris; 
and it was a matter of regret that I could not even spend an hour in giving it a detailed and 
careful examination, of which it certainly is most worthy, if for no other purpose than to study 
the extraordinary beauty of the great variety of volcanic rocks brought together in a manner so 
peculiar. It is possible that the highly inclined condition of the strata can be referred to a 
granitic intrusion in the mountains, but I am more disposed to refer it to some local intrusion of 
trap or porphyry which was not seen. 
Beyond this hill, we crossed several with rounded surfaces, but without seeing any rocks, and 
then reached the foot-hills of a granitic ridge trending parallel with the main chain, thus forming 
the northern boundary of a long valley. These foot-hills were not much elevated, and although 
nearly without timber or brush, are soil-covered, and support a growth of grass, which probably 
gives a cheerful green aspect to the surface in the spring and early summer, but which, in the 
fall and winter, assumes a sombre, uniform brown, or arid appearance. They have rounded 
surfaces, and appear to be formed of sedimentary rocks, although outcrops were not seen. As 
we passed over and among them, we came suddenly upon a large herd of antelope, quietly 
feeding in one of the depressions and on the hill-sides. There were probably not less than one 
hundred and fifty in the herd ; and, as soon as we were discovered, they bounded away most 
beautifully, and quickly disappeared over the top of the hill. 
Granite .—We passed from the rounded hills to the base of the ridge, which is formed of 
granitic or metamorphic rocks. Its surface on the northern side is, however, smooth, and 
nearly without trees or shrubs. These make their appearance, however, in the little valleys 
and depressions, especially where the ground is moist or springs issue. The underlying granite 
was not well exposed ; the soil was deep, and only an occasional outcrop was found. The rock, 
where seen, was hard and compact, and of a light-gray color. The minerals were disposed in 
lines,, and the trend was found to be N. 110° W. A broad cliff of this granite, with a bold, 
vertical face, near a spring, was covered over with strange hieroglyphic characters, the work of 
Indians, probably, many years before. One of these characters was like an anchor inform, and 
