COAST MOUNTAINS AND SIERRA NEVADA. 11 
the vicinity of San Pedro to San Francisco, and thence northward, the nearly uniform north- 
westerly trend of the parallel serpentine axes, the continuous series of Tertiary strata exhibiting 
similar lithological characters, and, in many cases, an identity of fossils, give a unity to the whole 
coast system. But at Point Concepcion the coast line leaves the general trend which it had 
preserved from San Francisco south, and is deflected far eastward, as though the Coast mountains 
had been cut away by the action of the ocean; and south of this point they ceased to exist, or 
were only represented by the islands which border the coast. 
At Los Angeles, and thence to San Diego, though still upon the Miocene Tertiaries of the 
Coast mountains, we were on their eastern, rather than, as before, their western base, and had 
approached to within a few miles of the Sierra Nevada. 
At San Diego the Tertiary rocks are exposed for several miles in the eroded channel of San 
Diego river. Here they are nearly horizontal, entirely unchanged, and contain great numbers 
of fossils. In speaking of the age of the Sierra Nevada, I shall perhaps have occasion to return 
to this subject, and to treat more fully of the geology of the coast near the southern boundary 
of the State. I may here say, however, in reference to the comparative ages of the Coast 
mountains and the Sierra Nevada, that while Tertiary strata, for the most part Miocene, but 
probably also including those of still more recent date, envelope the igneous axes and crown 
many of the highest summits of the Coast mountains, indicating that the elevation of this system 
was altogether posterior to the Miocene epoch; the Sierra Nevada bears no strata so recent on 
its summits, and scarcely on its sides, but is skirted on either base by Miocene rocks not much 
disturbed. This proves that the great mass of this latter mountain system, though doubtless 
in some degree elevated during or subsequent to the deposition of the Miocene series, had a 
distinct existence anterior to that epoch, and raised its summits far above the Miocene sea, to 
which it formed the boundary. 
The latest work which contains any notice of the geology of this region (Marcow’s Geol. 
NV. Amer., p. 79) presents so different a view of the structure of the Coast mountains from that 
which I have given that I am compelled to refer to it. Mr. M. says of the ‘‘ Coast Range 
System,” that it is composed of chains of mountains of slight elevation, generally from 500 to 
1,200 feet high; that it extends from Cape Mendocino to Cape St. Lucas, and probably includes 
the mountains of Sonora and Western Arizona ; thatits rocksare chiefly eruptive and metamorphic, 
containing mercury, silver, copper and iron, but no gold; that it is older than the Sierra Nevada 
system, and is characterized by Eocene fossils found south of Monterey and at Mount Diablo; and 
that hence the date of its elevation was after the Eocene and before the Miocene period.” In 
reference to these points, I have been led by my own observations, and by reliable testimony, 
to very different conclusions, namely: ? 
Ist. The Coast range system is composed of mountains of 2,000 to 6,000 feet in height; 
extends from San Diego, California, to Washington Territory; does not reach Cape St. Lucas, 
nor enter the peninsula; and is not found in Sonora or Arizona. = 
2d. Its surface rocks are chiefly sedimentary; gold is found in many parts of it, while silver, 
Copper and iron are, like gold, much more abundant in the Sierra Nevada. 
3d. It is of later date than the Sierra Nevada, and, so far as now known, has yielded no 
Eocene fossils; those of Mount Diablo and of the region south of Monterey, (Santa Barbara, San 
Pedro, San Diego, &c.,) considered such by Mr. Marcou, being all Miocene; hence the date of 
elevation of the Coast mountains is subsequent to the Miocene epoch. 
Of special interest in connexion with the elevation of its mountain chains are the more 
recent oscillations of level of which the southern coast of California bears evidence. I have 
elsewhere noticed the existence of a bed of recent shells upon the shores of San Pablo bay, 
many feet above the present water level; and have referred the profound erosion of the Golden 
Gate and the straits of Carquinas to a period of still greater elevation than the present. At 
several points on the coast of southern California I found evidences of recent elevation still more 
