18 AURIFEROUS GRAVELS OF THE SIERRA NEVADA, 
tween Sierra and Coast Range in that region, the exploration of which would 
be of great interest, as well as of great difficulty, owing to the thick under- 
growth on the mountain slopes, the heat and dryness of summer, and the 
remoteness from all lines of communication. 
In a rapid review of the geological characters of the Coast Ranges, we 
may begin at the southern extremity of the State and proceed northwards. 
Along the coast, from the boundary to the Santa Anna River, there is, bor- 
dering the ocean, a narrow strip of unaltered sedimentary rocks, of Creta- 
ceous, Eocene (?), Miocene, and Pliocene age. The region occupied by these 
rocks forms a “mesa,” some ten or fifteen miles in width, which rises gradu- 
ally with gentle slope to the base of a high, rough range of mountains, made 
up of granitic and highly crystalline rocks of the geological age, of which 
nothing is known. ‘The stratified rocks resting on these older crystalline 
ones are somewhat disturbed in position, but not metamorphosed. The 
granitic mass is broken up into various groups, of which the one at the head 
of the San Diego, Sweetwater, and Tia Juana rivers is called the Cuyamaca 
Mountains; its continuation north, between the San Bernardo and the San 
Luis Rey rivers, is known as Smith’s Mountain ; and from this north to the 
Santa Anna River as the Santa Anna Range. Northeast of these ranges, and 
forming their continuation in that direction, is the lofty mass of the San 
Jacinto Range. To the north of the latter, and separated from it by the 
San Gorgojio Pass, is the mass of which San Bernardino Mountain is the 
culminating point; then, again, farther west the San Gabriel Range, which 
connects with both the Coast Ranges proper and the Sierra Nevada at the 
nodal point near the Tejon Pass. These granitic and crystalline masses, 
which resemble those of the Sierra in being more or less auriferous, are un- 
doubtedly of much interest, but they have as yet been but imperfectly 
studied, and what is known of them has little bearing on the subject of the 
present volume. They, as well as the unaltered but somewhat uplifted 
sedimentary rocks at their bases, may be passed over without more notice. 
Starting then from the beginning of the Coast Ranges, as popularly desig- 
nated, in Santa Barbara and Ventura counties, we find the different ranges 
which have been previously mentioned — the Santa Monica, San Fernando, 
Santa Ifez, and San Rafael — to be chiefly made up of rocks of Miocene age, 
which are divided into two well-marked lithological groups; one a fine- 
grained slate or shale, often highly bituminous, and the other a rather coarse- 
grained sandstone, the latter being the inferior member. The Santa Monica 
