Clear Lake, although the great bituminous slate formation has been traced from Cape Mendocino through the country south to Los Angeles.

South of the bay of San Francisco the strata of this slate formation are everywhere turned up at a high angle, while north of the bay they are less disturbed. The tertiary, which is so limited north of San Francisco Bay, increases in importance going south. It flanks the cretaceous on both sides of the Mount Diablo range, and gradually limits it. The western and larger portion of the Santa Cruz range (the geology of which is somewhat complicated by the presence of intrusive granite rocks in various places, is said to be miocene. In the Gavilan and Santa Lucia system of ranges the tertiary is continued, and granite and highly metamorphosed rocks occur in considerable quantity; but the region is dry and very rough, and has been but little explored.

Asphaltum Deposits. The different ranges in Santa Barbara and Ventura counties are made up chiefly of miocene rocks, consisting principally of a coarse-grained sandstone below, and over this a fine-grained slate or shale, often highly bituminous and generally very much contorted and tilted nearly vertical. In Santa Barbara, Ventura, and Los Angeles counties, where the tertiary bituminous slate predominates, the principal deposits of superficial asphaltum have been found, and here attempts. have been made to strike flowing petroleum wells.

As one approaches the Sierra Nevada to the east of this region, and also in going south, granite becomes more frequent and the sedimentary rocks get harder and more crystalline. There is a granitic belt forming a continuation of the San Gabriel range, and connecting at Tejon Pass with the metamorphic and granitic masses of the Sierra, the crystalline rocks being apparently continuous, but the disturbance of the tertiary and cretaceous formations not being visible cast of Tejon Pass. The granite forming the divide between the branches of the

Santa Clara River and the Mojave Desert is overlaid on the edge next the plain with stratified beds of recent volcanic material.

Tin Ore. South of Los Angeles the ranges are of mixed character, and are very often considered as not belonging to the Coast Ranges proper. The Sierra de Santa Ana is composed on the south of granite, trappean and metamorphic rocks, while on the north coarse miocene sandstone and conglomerates prevail. The Temescal range consists principally of granite, porphyry, and metamorphic sandstone, partly cretaceous and partly tertiary. Here is the only known locality on the coast north of Mexico where tin ore has been found.

Still further south toward the Mexican boundary there is, along the ocean shore, a narrow strip of unaltered cretaceous and tertiary rocks.

Pliocene Gravels.-Pliocene gravels occur in various places in the Coast Ranges, sometimes in large deposits. These are in many cases the work of disintegrating adjacent formations. Gold has been found in some places, but seldom in paying quantities.

North of Clear Lake, at the bottom of the cañons which have been cut out chiefly by running water, are sometimes small deposits of gravel of pliocene age. These, especially at the north, carry gold. Between Clear Lake and San Francisco the only large gravel bed is the extensive one east of, and not far from, Clear Lake. This bed is covered in part by lava.

There are several localities in which deposits of gravel, probably pliocene, occur in the miocene strata of the Mount Diablo range, as scuth of the Livermore valley, but these contain no gold so far as known. Similar deposits are also found on the eastern edge of the Santa Cruz range, as on the east slope of the Mount Bache ridge, where considerable ground has been washed for gold, but without profit. Between the Gavilan and Mount Diablo ranges, south of Tres Pinos, there is an

immense mass of pliocene gravel, apparently non-auriferous, made up of pebbles of granite, red and green jaspers, silicious slates, and other metamorphic material. In the Santa Lucia range, near the Mission San Antonio, placers have been worked to some extent, and gold has been found in small quantities in several places.

The miocene strata of the ranges in Santa Barbara and Ventura counties are covered unconformably in places by nearly horizontal and slightly disturbed pliocene beds. In various places south of the junction, near Fort Tejon, of the Sierra Nevada and Coast Ranges, pliocene gravels occur over small areas. At San Francisco cañon these gravels have been washed and more or less gold obtained at various times since 1841 according to some authorities, and since 1838 according to Father Venegas.

Along the San Gabriel range gold-washing has been carried on intermittently with more or less profit. At the base of the Sierra de Santa Ana are immense accumulations of gravel made up of the wash of disintegrated tertiary strata.

Gold, Silver, and Copper Veins.-Veins of gold, silver, and copper have been reported at different localities along the Coast Ranges.

Eruptive Rocks.-A belt of eruptive rocks, of which Mount St. Helena is the culminating point, extends from near Napa to Clear Lake down to Suisun Bay, and large areas in this region are covered by lava, obsidian, pumice, and volcanic ashes. Especially in the vicinity of Clear Lake modern volcanic formations abound, and hot springs, sulphur beds, and other evidences of modern igneous action are common; but to the north of Clear Lake no volcanic phenomena of the kind are known, and south of San Francisco volcanic rocks are not found in any large quantities. Hot and sulphur springs are, however, quite common in the Coast Ranges.

THE GREAT VALLEY OF CALIFORNIA.

General Topography.-The valleys of the Sacramento and the San Joaquin rivers form in the centre of California a large plain, nearly elliptical in shape, extending from near Shasta, in lat. 40° 40' N., to Fort Tejon, in lat. 34° 50' N., an extreme length of four hundred and fifty miles, with an average width of forty miles, and an area of eighteen thousand square miles.

This plain is comparatively level. The Sacramento River, between Shasta and its mouth, has an average fall of 2.8 feet per mile. The San Joaquin River, from Kern Lake to its outlet, has an average inclination of 1.1 feet per mile. The valley of the Sacramento is narrower than that of the San Joaquin. The southern portion of the latter is very level and contains several shallow lakes of considerable area. The evaporation here about equals the water supply.

Drainage. By far the larger part of the water coming into the Great Valley is derived from the Sierra Nevada. There is hardly a stream which furnishes water throughout the year on the east slope of the Coast Ranges, certainly not one in the San Joaquin division. The fact that many rivers, passing chiefly through the mining regions, flow down the west slope of the Sierra and empty into the Sacramento or San Joaquin, makes the whole drainage system worthy of attention.

Rainfall. The rainfall of the Great Valley is comparatively small, especially in the southern parts. On the east slope of the Coast Ranges the amount of water derived from rain is small. On the west slope of the Sierra there is considerable precipitation, chiefly in winter, and in great part in the shape of snow. In the spring and early summer the flow of water down the last mentioned slope is greater than at other seasons, so much so that every year freshets occur. Heavy storms often cause destructive floods here, and if the theories of many

who have written on the subject of forests are correct, these floods will increase in magnitude with the destruction of timber in the Sierra.

THE BELT OF THE SIERRA NEVADA.

Topographical Structure.-The Sierra Nevada is a well-defined range of mountains situated on the edge of a high plateau, its eastern base being about four thousand feet high, while its western side slopes nearly to the sea-level. Its eastern flank is comparatively short and steep; its western, long and with a gradual descent, averaging in the central part of the State about one hundred feet per mile. This west side is broken by steep cañons in which the present rivers flow, running at about right angles with the axis of the ridge, so that an elevation of three thousand to four thousand feet above the sea-level the divide between any two streams is from several hundred to two thousand feet, or more, above the bottoms of the cañons on either side.

In the northern part of the State the range is outlined indistinctly, consisting of broken ridges with several prominent peaks. The general elevation may be assumed to be seven thousand or eight thousand feet. Mount Shasta, the highest point of this section, rises to a height of fourteen thousand four hundred and forty feet, dominating over all the others. South of this, from Lassen's Peak (lat. 40° 40′ N.) to near Tejon Pass (lat. 35° N.), the Sierra Nevada forms one clearly defined crest, gradually increasing in height toward the south. Along the headwaters of the Feather River, in Plumas and Sierra counties, the elevation of the prominent peaks is about nine thousand feet, and of the passes from five thousand to six thousand feet. Lassen's Peak rises ten thousand five hundred feet above the sea-level. The western slope here has a total width of some eighty-five miles.

Around the head-waters of the American River, in Nevada, Placer, and El Dorado counties, the main crest is