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much broken. Above them, along the margin of the plain, are beds of lava, increasing in width and having a northern dip, extending from the mouth of the Canada de las Uvas to the east and south a considerable distance. These seem to form a wall of division between the Sierra and the Coast Ranges. A range of undisturbed tertiary hills stretches to the northeast along the base of the Sierra Nevada from the Tejon Reservation —at the mouth of the Tejon Canon. To the southwest, this range extends towards, but does not connect with, the hills east of the San Emidio Canon, in which the strata dip at such a high angle.
In the preceding outline of the geology of the Coast Ranges, it will be seen that they have all been elevated since the deposition of the cretaceous. No older formation is known to occur throughout their entire length. In them every variety of structure is shown. The chains have been thrown up by forces acting in different directions, which have determined the trend of the mountain ranges, and of the coast. The most powerful seem to have been in a northwest and southeast direction.
It is only along the coast that thick forests occur; most of the hills and many of the valleys have scattered trees. The fertility of some of the valleys is marvellous; the bordering hills afford abundant pasturage.
Of the mineral wealth of the Coast Ranges, there is but little more to be said. Although gold, and ores of silver, copper and lead occur at various points throughout their extent, there is but little probability of their ever being found in quantity or under conditions to make them commercially valuable. Quicksilver is the great metallic product of the Coast Ranges, though its ore (cinnabar) occurs in rocks of almost every age. It is found in the Sierra Nevada, (Mariposa county); in Triassic rocks in the southern portion of the State; on the eastern slope of the Sierra—in strata of the same age, probably—and in the tertiary. Between Clear Lake, on the north, and the New Idria Mine, on the south, it is found at numerous localities—and it is in the motamorphic cretaceous alone, that large and valuable deposits seem likely to occur.
Of the non-metallic products, coal, borax and sulphur are the most important in an economic point of view. Although the former is known to exist at many different localities it is unlikely that any beds equalling in value those of Monte Diablo will be opened.
The deposits of chromic iron and manganese may hereafter prove valuable. Asphaltum exists in immense quantities, and petroleum has been obtained to some extent by tunnelling. The disturbed condition of the tertiary strata in which it occurs, is not favorable for its accumu
lation in interior cavities or reservoirs, and, up to the present time, the numerous attempts to obtain it by boring have not met with marked success.
GEOLOGY OF THE SIERRA NEVADA.
This grand mountain chain, bordering the eastern side of the great central valley of California, claims especial attention, not only on account of its magnitude and geological structure and the unsurpassed grandeur of its scenery, but because of the auriferous belt stretching along its entire western slope and constituting beyond a doubt the richest and most extensive gold field in the known world.
To the consideration of the structure of this chain, and of the great auriferous belt, speaking incidentally of some of the more important mines and mining districts, the remainder of this chapter is chiefly devoted.
The Sierra Nevada properly includes the San Bernardino mountains on the south, and stretches thence into southern Oregon on the north. It is a continuous and lofty chain, marked by a line of dominant peaks, many of which are over 14,000 feet high. It has an average width of ninety miles, being in places much wider. As has been stated, its western slope is more gradual than that of the eastern, which is often very bold and abrupt. On the west it is flanked by a long line of comparatively low foothills bordering the Sacramento and San Joaquin valleys. The "divide" or water-shed is generally on a line passing east of the line of culminating peaks mentioned in the remarks introductory to this chapter.
GEOLOGICAL STEUCTUBE OF THE SIERRA.
This range of mountains is known to consist of a central core of granite, flanked by metamorphic slates. In the southern portion granite is especially predominant, the highest summits and broadest mass of the chain being composed of that rock. The summits of the central portion are of metamorphic slates belonging to the eastern flank, and the culminating points in the northern part of the chain are of volcanic rocks. The western flank at an elevation of not over 1,200 feet, towards the south, and 1,000 towards the north, is marked at intervals, for a distance of over four hundred miles along the borders of the Sacramento and San Joaquin valleys, by the occurrence of undisturbed marine tertiary and cretaceous strata. These, though formerly continuous, are more extensively denuded and washed away in the central portion, than towards either end of the valley, where they are unbroken for long distances. south of the parallel of Sacramento the re strata, containing generally imperfect fossils, are extensively developed; further north, Cretaceous, with superimposed tertiary strata capped with volcanic outflows, are found resting horizontally upon the edges of the upturned auriferous slates. In the undisturbed position of these strata, as opposed to the extensive disturbances shown to have taken place in strata of the same age on the western side of the valley, we have the basis of Prof. Whitney's distinction between the Sierra Nevada and Coast Ranges; the State Geologist, considering all those chains or ridges of mountains as belonging to the Coast Ranges, which have been uplifted since the deposition of the cretaceous formation, while those, which were elevated before the epoch of the Cretaceous, are reckoned as belonging to the Sierra Nevada.
The tertiary beds which occur at a level of not over twelve hundred feet, and which are never worked for gold, are not to be confounded with the detrital deposits found high up on the flanks of the Sierra, which are of fresh water origin and form the great auriferous gravel beds of California. Soft tertiary sandstones are found all the way from White to Kern rivers, forming rounded hills from two to six hundred feet in elevation. From White river to King's river they are wanting, but from King's river as far north as the Stanislaus these hills recur, rising from one hundred to one hundred and fifty feet above the plain.
Cretaceous strata occur near Folsom, and at many points further north, being abundantly supplied with well preserved fossils. Between Feather and Pitt rivers, in the northern portion of the Sacramento Valley, is an extensive belt of cretaceous strata. Vast outflows of volcanic materials prevent, however, the underlying strata from being seen, except where the streams have cut them and exposed the sedimentary deposits beneath. In the Cretaceous strata between Cow and Clover creeks a workable bed of coal is reported to exist. It will, however, undoubtedly prove of but little economical value.
The region south of Cow creek is marked by the extensive deposit of volcanic materials. Lassen's Peak, and a large number of smaller extinct volcanoes between it and the Sacramento river, have been the sources of volcanic ashes, scoriae, and basaltic lava, which cover an area of seventy-five hundred square miles, lying between Pitt river and Oroville. The lava seems to have flown in sheets over the surface, and, between Fort Reading and Red Bluff, extends with a gentle slope westward to the Sacramento river. That the streams have in places cut entirely through the volcanic cappings, and into the Cretaceous strata beneath, is indicated by the occurrence of fossils of that age in boulders found in the canons and gulches.
Near Oroville, at Pence's ranch, the relation of the newer formations to the auriferous slates is finely displayed. The Cretaceous strata, with a low dip to the southwest, rest upon the edges of the upturned auriferous slates; upon the former lie tertiary strata, probably unconformably, though the disturbances have been slight, and these in turn are covered with tables of basaltic lava resting conformably upon them.
THE GREAT AURIFEROUS BELT.
Although auriferous rocks are not confined to the western slope of the Sierra Nevada, yet it is from the deposits and veins there found that almost the entire gold product of the State has been derived. The belt may be said to extend from Fort Tejon, northeast along this slope of the Sierra, into Oregon. The gold bearing belt of metamorphic slates within those limits varies greatly in width and richness. Towards its southern portion it is but feebly represented, but it widens out as it extends north. In the northern portion of the State it is almost entirely covered with vast deposits of volcanic materials, and in many places rendered inaccessible to the miner. It is the central portion of this belt that forms the great gold mining region of the State—a in the western portions of Mariposa, Tuolumne, Calaveras, Amador, El Dorado, Placer, Nevada, Sierra, and Plumas, and the eastern part of Yuba and Butte counties.
In the northwestern part of the State the auriferous slates are also exposed, but granitic rocks are there more extensively developed than in the central portion of the gold field, and the conditions for the formation of rich and extensive deposits have not been as favorable as elsewhere ; hence, in speaking of the main gold field, that portion of the State may be considered as of comparatively little importance.
SOUTHERN PORTION OP THE GOLD FIELD.
Between Mariposa county and Fort Tejon the granitic rocks of the Sierra descend lower down upon its flanks than further north, and the slates do not occupy a continuous belt, but occur in patches in the granite—although gold is found throughout the entire distance, and some rich placers have been worked at intermediate points, the veins of this portion must be considered as of inferior importance to those which are found in the broad and continuous belt of metamorphic slates extending to the northwest. Placer mines are worked to a limited extent in the Tehatchaypah valley, and in Walker's Basin. Near Kern river, are some promising quartz veins in granite, some of which have been worked with large profit. Arsenical pyrites occurs abundantly in these veins in the lower workings, causing trouble in milling the ores.
It was on the Mariposa estate, in this county, that some of the earlier quartz mining operations in California were undertaken. The western portion of the county is the more important, as being that traversed by the auriferous slate belt, in which are situated well known and extensively worked quartz mines. The eastern part is remarkable for the bold grandeur of its scenery, and contains several of the more lofty peaks of the Sierra. In this county is also located the famous Yosemite valley, elsewhere in this volume so fully described, that only a few considerations as to the cause of its origin will here be introduced. The volcanic accumulations being less extensive in this than along the gold belt in the more northern counties, no extensive hydraulic washings are carried on here—in fact, the yield of the placer mines in this county has been so much diminished that they may now be considered unimportant.
The Fremont Grant, now better known as the Mariposa estate, having from the first figured largely in the history of this county, still constitutes one of its prominent features. This estate embraces an area of about seventy square miles, extending from the Merced river, southeast, a distance of sixteen miles. It is traversed by a belt of metamorphic slates, with belts of generally highly metamorphosed sandstone on either side. Beyond the sandstone are slates again; serpentine and limestone occur in patches. Towards the southern end the metamorphism seems to have been greater, and granite cuts across the slate belt and continues westward towards the foot-hills. This belt is marked by the occurrence of numerous quartz veins which generally strike in a direction parallel to the trend of the enclosing strata, and dip with them. Veins in the granite to the south have the same general trend, a few degrees west of north.
There are several groups of mines within the limits of the estate. The Pine Tree and Josephine are located a mile and a half from the Merced river, and within a short distance of each other. They are generally considered to be on the same vein, though never having been connected, it is uncertain. They are remarkable for their enormous width of veinstone, which varies from twelve to forty feet, and in the latter averages twenty feet.
Six miles southeast of the Pine Tree and Josephine is another group of mines, of which the Princeton is the most important. This has in former years proved one of the most productive quartz veins of California. The trend and dip of the vein are the same as those of the enclosing strata. It varies in width, from a few inches to eight feet.