Slike strani
PDF
ePub

sandstone in the process of metamorphism, is the same as is usually associated with the ore. At the Lake mine, about eighteen miles from the southern end of Clear Lake, on the Suisun road, the ore is peculiar, on account of its association with sulphuret of antimony in acieular crystals and granular masses, as well as by reason of the absence of the peculiar silicious rock with which cinnabar is generally found. It is deposited in lenticular masses in cretaceous shales.

The locality known as the Geysers is half-way between Healdsburg and the southern end of Clear Lake. The wild scenery, and the phenomena exhibited by the hot springs occurring there, make it an attractive and interesting locality to visit; but there exists no analogy between these and the Geysers of Iceland. The waters hold a variety of salts in solution, which give rise to photo chemical reactions when waters from different sources are brought in contact, and produce vivid colorations of the rocks. These are chiefly sandstones and silicious slates, the silica of which is thoroughly leached out by hot alkaline solutions, and afterwards forms extensive deposits. Considerable quantities of sulphur are also deposited by the water from these springs, and the deposit known as the River bank, in the vicinity, may prove of future value.

One of the most interesting and curious portions of the Coast Ranges north of the Bay of San Francisco, is that in the neighborhood of the southern extremity of Clear Lake. It is in this vicinity that the celebrated and productive deposits of borax, or biborate of soda, occur beneath the waters of Borax Lake. This is a sheet of shallow water, the average depth of which is about three feet, comprising generally about one hundred acres in superficial area, but varying greatly in size with the seasons, as the shores are low, and their slope towards the water is very gradual. The water of the lake is impregnated with borax; analyses of it, made in 1863, show that it contained 2401.56 grains of solid matter to the gallon, about one half of which was common salt, one quarter carbonate of soda, and the remainder borate of soda, there being 281.48 grains of anhydrous biborate, equal to 535.08 of crystalized borax to the gallon. A sample taken from the interior of a coffer dam, from water percolating through the underlying mud, was found to contain a much larger portion of solid matter, but in the same proportion as before. The borax being the least soluble of the prominent ingredients, has crystalized out, and is found in the mud in crystals of various sizes, from two or three inches across, to those of microscopic size. That the process is rapid and still going on, is shown by the coating of crystals formed upon sticks of wood, which have been immersed in the waters of the lake for but a short time. The principal deposit of the crystals is in a layer of blue mud of varying thickness, beneath which is mud without them.

Northeast from Borax Lake, and about a mile distant from it, on the borders of Clear Lake, is an extensive deposit of sulphur, where solfatara action is yet apparent. The volcanic rocks have been extensively fissured, and through the orifices and seams, steam and sulphurous vapors are constantly issuing. A large amount of sulphur has been deposited, the extent of which is uncertain, and can only be demonstrated by the pick and shovel, though it occurs over an area of several acres. The most interesting fact in connection with this deposit is the association of cinnabar with the sulphur, sometimes distinctly separated from it, in quartz evidently deposited from solution, but often thoroughly intermixed with it.

Another large deposit of sulphur, about two miles distant, occurs on what is locally known as Chalk Mountain, so called from its peculiarly white appearance, and still another at the Sulphur Springs, further east, on the road to Colusa. At neither of these localities does the sulphur appear to be contaminated with cinnabar, which marks the deposit on Clear Lake. At the latter locality, which promises to be much more extensive than was at first supposed, a good merchantable article is being produced, in considerable quantities, by simple distillation. The rocks at Chalk Mountain are extensively fissured, and much decomposed, by the action of steam and acid vapor, giving them a white and chalky appearance. The deposit here promises to prove extensive, at least large superficial areas of it exist; how deep they will prove, or how large a quantity of sulphur they will yield, is of course a matter of uncertainty. "Springs yielding carbonated water are numerous in the vicinity of Chalk Mountain—it is often very agreeable to the taste.

Volcanic materials and hot springs occur on a line from Clear Lake east towards the Sacramento valley—and, as Prof. Whitney remarks, there is every evidence of a transverse fracture extending from the Geysers across the volcanic belt, of which Mt. St. Helena is the culminating point, to the Sacramento valley.

A curious association of gold, cinnabar, and bitumen occurs in what is known as the Manzanita tunnel, near Sulphur Springs, on the road from Clear Lake to Colusa. Beds of hydraulic limestone occur in the cretaceous strata near Benicia; they occupy a position between the sandstones and the shales.

The beautifully variegated Suisun marble occurs in the sandstones of the Pelevo hills, north of Suisun. It is the deposit of calcareous springs, and cannot be obtained in masses of sufficient size to make it very important as an ornamental stone.

[graphic]

SOUTH OF MONTEREY BAY.

North of latitude 35° 20' the trend of the mountain chains forming the Coast Ranges is quite uniformly northwest and southeast, agreeing very closely with that of the coast north of that parallel. South of this line, however, we have a very marked change in the direction of the coast . On the north side of Santa Barbara channel it runs nearly east and west, and near San Luis Obispo we have the northern limit of a system of upheavals, in a direction transverse to that which has determined the trend of the main Monte Diablo, and other ranges to the north.

The Santa Lucia mountains extend from Carmelo bay, near the town of Monterey, southeast in an unbroken line, bordering the coast as far as San Luis Obispo, then curving to the east, finally become merged into the main Monte Diablo Range. They form bio mass of rugged and unexplored mountains, in places over 5,000 feet in elevation. The western slope of the range is peculiarly abrupt and inaccessible.

The comparatively broad valley of the Salinas river, included between the Santa Lucia and Gavilan mountains, stretches to the southeast from the Bay of Monterey, a distance of nearly one hundred miles. The average breadth of the Santa Lucia range is about eighteen miles. Granite is known to occur throughout the northern twenty or thirty miles. Metamorphic tertiary rocks, and Miocene and Pliocene strata, highly contorted, also occur.

The Polo Scrito hills, between the valley of the Carmelo river and that of the Salinas, and the San Antonio hills further south, are made up of the great bituminous slate formation of the tertiary age, which extends through California as far north as Cape Mendocino; above which are more recent formations. Portions of the Tertiary are highly bituminous, and asphaltum is of frequent occurrence. Well marked re occur on the Salinas and its branches—the San Antonio and Mascimiento rivers. Near San Luis Obispo the range has a fan-like structure. Gold has been found in very limited quantities, and, at various points, copper stains occur; argentiferous galena is also found, but neither is likely to prove of importance—no well defined vein having been seen.

The islands on the south side of Santa Barbara channel appear to belong to the east and west system of upheavals, and are probably of the same geological age as the Coast Ranges. South of San Luis Obispo is a succession of mountain chains, having an easterly trend.

The Santa Ynez Range commences at Point Concepcion, stretching east a distance of over one hundred miles, and joins with mountain ranges south of Fort Tejon. East of Santa Barbara it attains an elevation of about 4,000 feet, but to the west it is lower, and at Gaviote Pass it is about 2,500 feet in height. The western end is composed of unaltered tertiary sandstones of miocene age. There the strata dip to the south; further east an anticlinal axis is shown, while still further east all the strata dip to the north.

Near Santa Barbara the sandstone, forming the crest of the chain, is overlaid by bituminous shales, which, in the foot-hills, are very much broken and contorted. Upon the bituminous shales, resting horizontally and unconformably, are pliocene and post pliocene deposits. The bituminous shales are the source of considerable quantities of bituminous material—asphaltum and oil occurring at many different localities, often filling depressions in superficial deposits; the latter is sometimes seen oozing from the shales.

Two minor ranges, lying between the Santa Lucia and Santa Inez chains, are, so far as known, almost wholly made up of tertiary strata of miocene and pliocene age, attaining a great thickness. More recent deposits in the valleys rest horizontally upon the edges of the upturned tertiary. Here also asphaltum and oil are of frequent occurrence.

In the Santa Susana Eange, which is, as far as known, composed of sandstones of tertiary age, upon which rests the bituminous slate formation, we have an instance of an enormous fault, which forms the San Fernando valley. The strata dip to the north, towards the valley of the Santa Clara river; the broken edges are presented to the south, rising like an immense wall from the plain. That this fault exists, is proved by the fact that the upper members of the same series of tertiary strata sink beneath the plain from the northern slope of the Santa Monica Bange, further south. The latter terminates in a bold headland on the Pacific ; it stretches east from Point Duma a distance of about forty miles. In this chain is shown a regular anticlinial axis—a central core of granite, with strata dipping away from it on both sides; these, consisting of sandstone and bituminous slates of miocene age, are much altered, more particularly so, however, when they are in contact with the central mass of granite.

The present geographical and geological knowledge of

[graphic]

part of the State is extremely limited. The San Gabriel Range is a mass of high and rugged mountains extending from the Cajon Pass, on the east, to the Santa Susana and Santa Monica Ranges on the west . They are largely composed of granitic and metamorphic rocks. North of Los Angeles two high points of granite rise to about 5,000 feet. At the base of the mountains tertiary sandstones have been exposed by erosion; above them are masses of post tertiary detritus piled up against the flanks of the range to heights of over 1,000 feet. The rocks occurring in the San Gabriel Canyon are highly metamorphic, and probably belong to the cretaceous period.

East of the San Gabriel Canyon, on the southern flank of the range, are immense masses of tertiary sandstone, highly disturbed, and traversed by numerous dykes of granite. Both copper and silver ores have been found in this range. Gold has been mined to some extent—though with no great profit.

To tho south are the Santa Ana and Temescal Ranges. The latter has attracted considerable attention, on account of the discovery of tin ore about three miles north of the Temescal ranch-house. It is peculiar in appearance, and is probably a mixture of cassiterite (oxide of tin) and more or less earthy and mineral matter. Explorations have as yet failed to develop deposits of any material value. The geological age of the rocks in which it occurs is not known.

As before stated, a perfect topographical union of the Coast Ranges and the Sierra Nevada takes place at the southern end of the Tulare valley. The lowest pass from the Tulare valley to the Great Basin, though there is no well marked one, is that taken by following up the north fork of the Tejon Creek and crossing a low ridge into the Tahatchaypah valley. In this route the highest point attained is about 4,000 feet.

The San Emidio Canon, about twenty miles west of the Canada de las Uvas, opens into the valley of Kern and Buenavista lakes. Toward the head of this canon, granite, mica-slate, syenite, hornblende slate, and limestone are found. An inconsiderable thickness of Cretaceous strata, overlaid conformably by an enormous development of unaltered tertiary, rests on these. The strata dip to the north at an angle of about seventy degrees. The belt of tertiary extends east along the flanks of the mountains, and terminates in a range of hills northwest of the Canada de las Uvas. At this canada cretaceous strata also occur; they are better shown, however, in the Canada de los Alisos, opening into the plain about five miles further east. At this place tho cretaceous bolt is of greater width, and the strata are well exposed, though

« PrejšnjaNaprej »