A large part of the area is underlain by sedimentary strata of a comparatively recent geological age. Triassic and Jurassic beds pre dominate in the northern and west-central parts, and Cretaceous and Tertiary beds in the coastal region. Along the Sierra Nevada and Coast ranges volcanic rocks are strongly developed and cover wide areas. The central axes of these two great ranges are formed, however, by ancient ig neous andThietamorphie rocks which may belong to the _Archaean formation. Granite is especially prominent in these localities and constitutes some of the highest peaks. The elevation of the Coast Range took place at the close of the Miocene period, while the Siernis were formed largely by an uplift that occurred near the end of the ,Juras sic period. Carboniferous strata occupy a large area in the central part of the State, but they inclose no eoal-seams of economic importance.
California is rich in mineral de posits, particularly gold, which is found in over thirty counties, and the rapid settlement and development of the State were due to this fact. (;old was obtained by washing as early as 1S-11, near San Fernando mission; but it was the dis covery at Sutter's Mill, near Coloma. in 1S4S, that made evident the abundance of the metal and attracted the excited throngs of adventurers. Many of these engaged in river mining—Le. washing in sheet-iron pans or wooden 'rockers' the gold from the sands or gravels from or near river channels; others dug the gold `dry' from veins in the rocks. About 1351 sluices were introduced, by means of which the gravels or sands were run over the bottom of a wooden box provided with blocks of wood or round stones to catch the gold as it sank. Digging soon ex tended from the rivers and the gulches to the higher ground, where the difficulty of washing was increased; but in 1S52 the hydraulic system was brought in. In this, continuous powerful streams of water are directed through nozzles upon a gold-bearing bank or deposit. This was so successful that whole hills were reduced and swept away, but this practice was soon forbidden by law, as the detritus threatened to choke the rivers and seriously damage the agricultural in terests in the valleys below. Nearly all the mines are on the western slope and in the foothills of the Sierra Nevada in a belt of country about 220 miles long by 40 wide, extending into Oregon. The gold is found in a metallic condition, but is usually mixed with silver or other metals. In stream or alluvial 'deposits ('placers') it oc curs as fine scales or coarse grains. In rocks, it is found in quartz veins, and costly machin ery must be used to crush the ore, from which the gold is extracted by amalgamation with quicksilver. Where, as often is the ease, the gold bearing gravels underlie volcanic rock several hundred feet thick, drift or tunnel mining com bined with sluicing is necessary. The chief gravel mining region extends from Mariposa County into Plumas County. or between parallels 37° and 41°, and includes seine quartz veins. Most of the gold is now obtained from the quartz mines, especially in C'alaveras. Kern, Trinity, El Dorado, Nevada, and Sierra counties. Gold mining is to-day greatly facilitated by the appli cation of electrical power. which the mountain streams are made to generate. The great promi
nence and significance of gold in the early years of the State are evident from the great size of the output, the annual average for the decade be tween 1850 and 1859 inclusive being estimated at over and constituting nearly the entire product of the United States. Following this period there was a constant decline in the output, which reached the minimum ($12.000, 000) in 1802; it then revived, and for the last half-deeade of the century averaged over $15, 000,000 annually. The State continued to hold first place until 1897, when it was surpassed by Colorado. The total output of the State to the end of 1900 was about $1,350,000,000. While rich silver ores are found, there are no mines which produce silver exclusively. The $700.00 of silver mined in 1900, an increase over former years, was a by-product from gold, lead, or copper mining. Copper-mining has recently made rapid progress, and the State ranks fourth in the pro duction of copper ore, the yield having, in creased from 6300 tons in 1897 to 13.200 tons in 1900. This ore, which is found principally in Shasta County, is partly shipped out of the State for smelting.
The State produces almost the whole of the quicksilver output of the United States, its mines rivaling those of Spain in productive ness. From 1875 to 1S82 the output averaged 64,000 flasks annually, but since that period the annual average has been only 30,000 flasks: the value of the product ranged from $1,000,000 to $1.500,000. Fifty per cent. of the product is se cured from Santa Clara County. The fuel prod ucts of the State include petroleum, bituminous coal, and natural gas, of which the first is the most important. The oil is found in the southern coast region, particularly Los Angeles, Kern, Santa Barbara, and Ventura counties. It is re fined to some extent, but its most important use is as a fuel. Its production is steadily increas ing, the output having grown from 300.000 bar rels in 1890 to 4,250,00 barrels in 1900. Bitu minous coal is mined in Monte Diablo and the neighboring hills. For several years the output fluctuated around $200,000 in value, but for a fewyears now the annual output has doubled that amount. Natural gas is found in the Sacramento and San Joaquin valleys. The State ranks second in the production of mineral water. the product for 1899 having been estimated at $695, 000. Salt is obtained by the evaporation of sea water. Building-stone is abundant, and includes hydraulic limestone, rhyolite, bluish and light brown sandstones from San Francisco Bay, and from San Josts a light-brown variety, which is al most pure silica, cuts easily, and stands fire well. San Bernardino County yields marbles of many shades; El Dorado County, fine white marble, streaked with blue; and in Ingo County some of the foothills are composed of white marble equal to Italian. Freestone, huh granite, and basalt suitable for pavements and buildings are also found in abundance, while the granite output averaged in value about $1.000.000 an nually during the last decade of the century. Brick clays occur in some localities. Asphalt is obtained in varying quantities and constitutes the greater part of the output of the United States, the largest annual product, that for 1898, exceeding $600,000 in value.