Statewide County CA Archives History - Books .....Drift Mining In California 1891 ************************************************ Copyright. All rights reserved. http://www.usgwarchives.net/copyright.htm http://www.usgwarchives.net/ca/cafiles.htm ************************************************ File contributed for use in USGenWeb Archives by: Joy Fisher sdgenweb@gmail.com November 28, 2005, 7:41 pm Book Title: Memorial And Biographical History Of Northern California DRIFT MINING IN CALIFORNIA. This article is from the pen of Russell L. Dunn, in the State Mineralogical Report: Drift mining is peculiarly a California development of the gold placer-mining industry, originating from the exceptional conditions of location of the larger area of these auriferous deposits. The placers by geological age and local condition are generally divisible into two classes. First, the so called blue-lead or ancient river channel placers, the result, of river wash and erosion of the pliocene or quarternary age, or of both, geological authorities differing. Second, the recent deposits of existing streams. The latter, though covering a wider range of country than the older placers, are comparatively limited in aggregate area, being for the most part the river and stream beds and their banks and bars. Being accessible and workable by primitive methods without the need usually of any capital, except that of labor itself, they were readily discovered and rapidly worked out. The gold they contained came very largely from the blue-lead ancient river channels that were cut through and eroded away by the present river system. A small portion only seems to have come from the direct disintegration by these streams of the auriferous slates, talcose rocks, and quartz lodes. Though some of the deep bars and portions of their channels that have been covered by slides are worked by the methods and appliances of drift mining, it is with the remains of the ancient river channels that the industry is most closely connected. Geographically, the ancient river system, whose buried channels are so auriferous, extended from what is now Butte and Plumas counties on the north to Tuolumne on the south, and from the eastern edge of the Sacramento Valley almost to the summit of the Sierras. Within these limits are included portions of the counties of Butte, Sierra, Plumas, Yuba, Nevada, Placer, El Dorado, Amador, Calaveras, Tuolumne and Stanislaus, in all (roughly approximated) an area of 7,000 square miles, only a small portion of it, however, being actually covered by the remains of the ancient channels. The topography of this section has been formed by tributaries of the Sacramento rising at the summit of the Sierras and flowing in the precipitous conons of their erosion, till the Sacramento Valley is reached. Starting at the valley, the beds of these canons rise from ten to forty feet to the mile for the first forty or fifty miles, thence with much steeper grades to the headwaters, only a thousand or so feet below the summit of the Sierras. The narrow ridges between the canons rise from the plains with mean grades of from 100 to 150 feet to the mile, to summit elevations of from 0,000 to 8,000 feet. The topography of the country during the existence of the pliocene and quarternary rivers cannot now be restored with more than probable certainty. It seems likely that the river system then was very similar to the present one in relative location and direction of flow of the main streams, at least particularly through the northern portion of the district. At Oroville, in Butte County, is the debouchure of a great river coming from the north and corresponding to the present Feather River, and apparently draining much the same territory. At Smartsville, in Yuba County, is the evidence of an ancient river the counterpart of the present Yuba. The main stream can be traced up the "Ridge," as it is locally known, lying between the Middle and South Forks of the Yuba to about Moore's Flat, thence northward into Sierra County. Remains of what must have been its tributaries are observable all over northern Nevada County and central and northern Sierra into Plumas County. In Placer County, from Auburn southwesterly, there are the remains of an old river channel, the predecessor of the present American. Higher up in the mountains there is a tangled network of old channel fragments that were once part of its system. Further south at La Grande, in Stanislaus County, is the outlet for the pliocene rivers of Tuolumne and probably Calaveras and Amador counties. A careful study and comparison of the location, direction, elevation, and grade of the remains of the channels is convincing that there is not one main great blue-lead channel coming from north to south, as supposed for many years after the mines in them were discovered and worked, with tributary channels coming in from the east and the west, a system analogous to the main Sacramento, but in the mountains fifty miles east of it, but that, as already stated, the system was much the same as at the present time. In the northern portion of the district the channels can be traced for long distances, have indeed been somewhat restored by mining operations in them and their continuity and identity established with considerable certainty. In the southern portion the remains of the old channels are very fragmentary, either as a result of more complete subsequent erosion, or because the system originally was not as extensive or permanent. A complication of the problem of identity of the more or less; isolated fragments of these channels comes from in disputable evidence that there were two, and in some localities more, systems formed necessarily in different periods of time. The ancient streams, as indicated from the immense masses of drift gravels and detritus they have left in their channels, probably carried much larger volumes of water than the present streams. The mean gradient of their beds was considerably more than that of the existing streams at corresponding points, for, although in the enormous lapse of time great local changes in elevation are possible, it is almost certain that the elevation of the Sierra Nevada mountain chain to substantially its present condition and altitude was in the later cretaceous or early tertiary periods. The changes in it have been the result of glacial and stream erosion and of lava flows, not, so far as the section under consideration is concerned, of local genesis. The periods of erosive energy of the ancient streams were not as long as that of the present, as they evidently did not cut as canon-like depressions. The general surface of the country was not, therefore, as rugged as now, being hilly rather than mountainous, the difference in altitude of the general plane of the surface of the country and the stream channel depressions at corresponding points being much less than at the present time. The gold in the channels is the product of the primary disintegration of the auriferous slates, talcose rocks, and quartz veins. Whether or not these disintegrated rocks were richer in gold, and the eroded portion of the veins more massive, is uncertain, but the erosive agencies of water and cold were undoubtedly much more powerful then. The theory of direct glacial erosion is hardly tent able, as no trace of it appears in the channels, and remains of flora and fauna are found that indicate, if not a temperate, certainly a subarctic climate. Le Conte says that the glacial erosion was prior to the formation of the channels, and was the greater disintegrating force. The great changes in the location of the stream channels have been made by eruptive agencies. A secondary cause was their filling up with accumulations of gravels, sands, and clays. Enormous flows of trachytic lava (trachyte after Ashburner, Geological Surveyor, California—andesite after Becker, United States Geological Surveyor), volcanic ashes, tufa, and mud coming from the north filled up the channels at some points to several hundred feet in depth, turning the streams and completely altering the surface of the country. This covering up and obliteration of the surface was not the result of one season of eruptive activity, but of several, separated by enormous intervals of time only less than that which has elapsed since the final dying out of the plutonic forces. Discussion of this volcanic action is somewhat speculative, and deductions from the indeterminate phenomena are uncertain. As an opinion, merely based on examination and comparison, it is true the first of the flows in point of time seem to have consisted of trachytic lava, and to have covered the greater territory; that there then followed a long period of inactivity of the interior forces, during which the streams adjusted their channels to the changed topography. The first flows probably did not completely divert the streams, except at a few points, but merely raised their beds and changed the character of the channel deposits, the latter becoming largely lava. The period of inactivity was in time followed by another display of the plutonic forces, and in its turn by a period of quiescence. This sequence, repeated several limes, but with a diminishing power and range of the eruptive energy confining it more and more to the northward, and with lengthening intervals of repose, finally ended in the complete cessalion of the eruptive energy. These latter flows, in addition to the trachytic lava, consisted largely of volcanic ashes and tufa, and volcanic mud. The channels and surface depressions generally, and some of the lower hill elevations, became more and more filled up and obliterated, until at the end of the last period of eruption a completely new topography was forming, the beginning of the present. The lessening area to the south covered by the successive flows accounts both for the greater erosion of the eruptive deposits of the southern portion of the district, and for the greater aggregate depth and more numerous strata of the northern portion. It is probable that many of the existing river channels are the original ones cut deeper into the country rock, the volcanic flows not obliterating them at all, or only temporarily. This is particularly the case in the lower courses of the larger streams. The geological time of the end of the eruptive period was probably in the earlier quarternary, prior to the glacial epoch or age of ice. During it and since then has been the erosion of the existing river system. This, as before stated, is a system of tremendous gorges and canons cut down through the surface volcanic deposits, the drift-filled old river channels, and from a few hundred to three thousand feet into the country rock. An erosion so stupendous could hardly have been made by the narrow, small, flowing streams now in the bottom of these canons, conceding almost any geological lapse of time. Only glacial action followed by great torrential streams can account for it. The old river channels now are—as the result of the eruptive flows first filling, then denudation by glacial and stream erosion, depressions in the surface of the country rock filled with river sands, gravels, and clays, and capped with lava, volcanic ashes, and tufa, with possibly wash gravels lying between the volcanic flows—the remains of stream erosion in the interval between the flows. The depth of the gravels on the bed-rock will vary between limits of nothing to three hundred feet; the depth of the volcanic flows and other gravel deposits from nothing to fifteen hundred feet; though at no two points would exactly the same deposits, either in quality or relation, be found. The following data from the shaft of the Gray Eagle Drill Mine, Sec. 6, T. 13 N., R. 10 E., M. D. M., near Forest Hill, Placer County, is typical, and well illustrates the phenomena of several of the eruptive periods and the stream flows of the intervals between. Beginning at the surface, in sinking, the shaft passed through— Red soil and loam 10 feet. Soft gray volcanic ash 31 feet. Hard gray lava, containing angular fragments of Slate 80 feet. River wash, sand and gravel in alternate strata, principally sand 34 feet. River wash, gravel and sand in alternate strata, principally gravel 30 feet. Yellow water sediment, pipe clay 25 feet. Loam, fine black sediment, containing leaves, logs, etc 10 feet. Large bowlders, water-worn 10 feet. Hard, chocolate-colored lava 60 feet. River wash, gravel and sand 10 feet. Hard, chocolate-colored lava, containing logs, some petrified 20 feet. River wash gravel 7 feet. Hard, chocolate-colored lava 25 feet. At this point the country rock is struck sloping down, showing that the bottom of the channel has not been reached. On and in this rock gold was found. In this particular case there are four distinct lava flows determinable and four river flows in substantially the same channel. Not till the channel became full by the last volcanic flow did the old stream take an entirely different location. Comparatively few shafts have been sunk through these lava flows, the mining of the auriferous gravels underneath being most practicable through tunnels, and in the sinking of the shafts but little attention has been paid to keeping a record of the character of the ground passed through. However, in the working of some of the drift mines through tunnels, several of these lava flows have been located far underground, not superimposed one on the other, but filling channels that have cut through and crossed older channels filled with older lava flows. In the Bald Mountain Mine, at Forest City, Sierra County, the channel being mined was crossed and cut through by another channel about five hundred feet wide. The latter was filled at the bottom with a kind of volcanic mud and contained no gold. In the Mountain Gate Mine, at Damascus, Placer County, a wide white quartz channel was found to be cut through and crossed by another channel over five hundred feet wide and sixty feet lower at the crossing. This last channel, unlike that in the Bald Mountain Mine, contained auriferous blue gravel (almost exclusively slate) from six to fifteen feet in depth, directly overlaid with a hard, compact lava. In the Paragon Mine, at Bath, Placer County, there are three distinct determinable channels. First, the lowest and original, a blue gravel channel lying directly on the country rock. Second, an upper channel one hundred and fifty feet above the first in an elevation and having the same general line of flow. Between the two are alternate layers of wash gravel, sand, and pipe clay. Third, a channel crossing and cutting through the second, but not down to the first. This last is filled with a lava flow. Some of these old river channels are filled to depths of several hundred feet with gravel, sand, and pipe clay, all river deposits, which extend to great widths and far beyond the limits of the lowest channel depression. Additional Comments: Extracted from Memorial and Biographical History of Northern California. Illustrated, Containing a History of this Important Section of the Pacific Coast from the Earliest Period of its Occupancy to the Present Time, together with Glimpses of its Prospective Future; Full-Page Steel Portraits of its most Eminent Men, and Biographical Mention of many of its Pioneers and also of Prominent Citizens of To-day. "A people that takes no pride in the noble achievements of remote ancestors will never achieve anything worthy to be remembered with pride by remote descendents." – Macauley. CHICAGO THE LEWIS PUBLISHING COMPANY 1891. 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