the whole of the agricultural and the greater part of the mining districts.
These
lines divide the State geologically as well as physically. The Great
Valley is the belt of recent alluvial deposits ; the Sierra is the
belt of intrusive granite, of strata principally of triassic and
Jurassic age, with important pliocene river deposits, of
ante-cretaceous elevation, and of metamorphism induced by heat and
pressure and resulting in a hard and crystalline condition of the
rocks; the Coast Ranges form the belt of strata chiefly of cretaceous
and tertiary age, of post-cretaceous elevation and of chemical
metamorphism.
The
Sierra is the belt of the precious metal, with some iron and copper;
the Coast Ranges, principally of quicksilver and carbonaceous
materials. The Sierra is the region of lofty heights, the Coast Ranges
of moderate elevations, and the Great Valley of nearly dead level.
In the Sierra volcanic activity has ceased, but in the Coast Ranges solfataric action is still apparent.
This parallelism does not exist in the northern and southern parts of California. North of lat. 400
N. the Sierra and Coast Ranges approach one another and finally
connect, the distinction between them being not yet definitely
settled. In the south the Sierra swings to the west and joins,
physically at least, with the Coast Ranges, which here, following the
coast line, trend to the east. Thus the Great Valley is closed in its
upper and lower extremities. The northern and the southern portions of
the State have not been thoroughly examined, and the present knowledge
of their topography and geology is very limited.
The
map accompanying this work shows the mountain ranges where the
auriferous gravels exist and also the streams draining the hydraulic
mining districts.*
*
The map was compiled from the latest official surveys by William
Hammond Hall, State Engineer of California. For the purposes of this
work certain additions have been made by the author.
