The Sierras have a structure and a physical character which are individual and unique. To Professor Whitney and his corps of the Geological Survey of California is due the honor of first gaining a scientific knowledge of the form, plan, and physical conditions of the Sierras. How many thousands of miles, how many toilsome climbs, we made, and what measure of patience came to be expended, cannot be told; but the general harvest is gathered in, and already a volume of great interest (the forerunner of others) has been published.
The ancient history of the Sierras goes back to a period when the Atlantic and Pacific were one ocean, in whose depths great accumulations of sand and powdered stone were gathering and being spread out in level strata.
It is not easy to assign the age in which these submarine strata were begun, nor exactly the boundaries of the embryo continents from whose shores the primeval breakers ground away sand and gravel enough to form such incredibly thick deposits.
It appears most likely that the Sierra region was submerged from the earliest Palæozoic, or perhaps even the Azoic, age. Slowly the deep ocean valley filled up, until, in the late Triassic period, the uppermost tables were in water shallow enough to drift the sands and clays into wave and ripple ridges. With what immeasurable patience, what infinite deliberation, has nature amassed the materials for these mountains! Age succeeded age; form after form of animal and plant life perished in the unfolding of the great plan of development, while the suspended sands of that primeval sea sank slowly down and were stretched in level plains upon the floor of stone.
Early in the Jurassic period an impressive and far-reaching movement of the earth’s crust took place, during which the bed of the ocean rose in crumpled waves towering high in the air and forming the mountain framework of the Western United States. This system of upheavals reached as far east as Middle Wyoming and stretched from Mexico probably into Alaska. Its numerous ridges and chains, having a general northwest trend, were crowded together in one broad zone whose western and most lofty member is the Sierra Nevada. During all of the Cretaceous period, and a part of the Tertiary, the Pacific beat upon its seaward foot-hills, tearing to pieces the rocks, crumbling and grinding the shores, and, drifting the powdered stone and pebbles beneath its waves, scattered them again in layers. This submarine table-land fringed the whole base of the range and extended westward an unknown distance under the sea. To this perpetual sea-wearing of the Sierra Nevada base was added the detritus made by the cutting out of cañons, which in great volumes continually poured into the Pacific, and was arranged upon its bottom by currents.