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Title: The Tertiary Gravels of the Sierra Nevada of California by Waldemar Lindgren (1911) Collection Type: Books and Periodicals Source(s): Google Books # of Pages: 301 Download PDF: User Login Required Download OCR Text: User Login Required

Date Scanned: 2024-07-14 06:26:22 Item Sourced From: PDF First Created: 2025-03-17 05:53:20 Last Updated: 2025-03-17 05:53:20

Original Held At: Searls Historical Library Location: 161 Nevada City Hwy, Nevada City, CA 95959

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86 TERTIARY GRAVELS OF THE SIERRA NEVADA OF CALIFORNIA. VALUE OF THE GRAVELS. The bottom gravels of the Neocene channels are usually rich, values of $3 to $6 a cubic yard being common. Most of the operations are, however, conducted on a small scale, for the channels are mostly narrow and the bedrock uneven. The drift and hydraulic mines of the Chico quadrangle vary considerably in ‘production from year to year. There are ordinarily from 15 to 25 operators, and the total yearly output ranges from $100,000 to $200,000, the latter figure being nearly reached in 1901. The largest individual production during that year was $52,000. In 1908 the production of the same class of mines was reduced to about $26,500, only about $14,000 being reported from drift mines. Besides there is an output of gold from ‘‘surface mines,’”’ mainly Quaternary, which in 1908 yielded $56,000. In 1909 about the same production was recorded. TABLE MOUNTAIN AND OROVILLE. Table Mountain, north of Oroville, is of especial interest owing to the presence of gravels of many different ages. The geologic history is briefly as follows, beginning with the oldest deposits: (1) Deposition of Chico formation (Upper Cretaceous); (2) epoch of erosion; (3) accumulation of lowest gold-bearing gravels + (KEocene?); (4) deposition of Ione formation, underlying Table Mountain; (5) eruption of basalt of Table Mountain; (6) formation of high volcanic gravels of Table Mountain; (7) epoch of erosion; (8) deposition of tuff and lower gravels (late Pliocene) of Oroville; (9) epoch of erosion; (10) deposition of bench gravels of Oroville (Quaternary); (11) epoch of erosion; (12) deposition of present stream gravels. (See Pl. XV.) There is only one small exposure of the Chico formation in Dry Creek, a mile south of Pentz’s ranch, at the northern base of Table Mountain, at an elevation of 300 feet, and the Cretaceous sandstones are here covered by beds containing shells of Corbicula, a fresh or Figure 4.—Diagrammatic section of Tertiary gravels, Ione formation, brackish water mollusk. The fossiliferous beds Coun Bel Eeweter sxplune, Oroville Table Mountain, Butte are in turn covered by the thick white clays and shales of the Ione formation. A few miles north of Pentz, in Big Butte Creek, the Chico attains an elevation of 1,000 feet, but south of Table Mountain the Ione formation rests directly on the bedrock. The well-known Cherokee hydraulic mine (Pl. IV, p. 24) is situated at the north end of . Table Mountain and has been described briefly by J. S. Diller ? and in several of the reports of the State mineralogist.2 The bedrock of the channel mined is exposed for about 4,400 feet, and in this distance the descent is 250 feet in a west-southwest direction. The form is that of a flat trough, the bedrock rising on the south side 150 feet and on the north side 200 feet and being laid bare throughout. Many millions of cubic vards of gravel have been removed. The bottom of the channel is on the whole flat and 700 feet wide. The bedrock is very irregular in detail and covered by large greenstone bowlders. The elevation at the upper or east end is about 1,250 feet; at the lower end, at the hydraulic bank, about 1,000 feet. This channel is not the bed of a main river but rather that of a broad and steep gulch. The succession of beds is shown in the accompanying diagram (fig. 4). The following is the section, beginning from the bedrock: 1 ihe Tom To ut coon TAREROREI TW OORATINGANGON//ONORRON I ViGNONOI IIANEG] RECENT TM 5) CECE Intl! MMU a ttl at MH UsUH MOOT SO CO TTT TTT f i TA i . . HAIL 360 feet Hh {. . 1 1 Turner, H. W., The rocks of the Sierra Nevada: Fourteenth Ann. Rept., U. S. Geol. Survey, pt. 2, 1894, p. 403. 2 Tertiary revolution in the topography of the Pacific coast: Fourteenth Ann. Rept. U. S. Geol. Survey, pt. 2, 1894, p. 418. 3 Notably by E. B. Preston, in Eleventh Rept., 1893, p. 135.