Collection: Books and Periodicals

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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

Page: of 301  

144 TERTIARY GRAVELS OF THE SIERRA NEVADA OF CALIFORNIA. covered with deep clay on the south side. A little work has been done on all of them. It is said that at Coopers Mill an old incline was sunk on the rim, tracing the bedrock down to an elevation of 3,500 feet. If this report is correct it is highly remarkable, as this elevation is considerably lower than the rim rock at any other point in this lava area and would imply the existence of a closed basin. The important Centennial-San Jose channel is covered by this same lava area. Buckeye IIill is a small mass of bench gravel southeast of Quaker Hill. The gravel has been almost entirely removed. YOU BET AND LITTLE YORK. At Red Dog and Hawkins Canyon, near You Bet, the deep channel has again been exposed and is beyond doubt continuous between the two points. The gravel is similar to that of Quaker Hill. The deepest gravel has been hydraulicked only at the places mentioned, but considerable drifting by means of tunnels and inclines has been done from Niece & West’s claims for 14 miles northeast, on the Steep Hollow side. The channel has very little fall, the average elevation being 2,620 feet. Over a part of the distance where the direction of the river was northeasterly the grade is reversed. It is estimated that 47,000,000 cubic yards of gravel has been removed, leaving over 100,000,000 yards available. Much of this, however, would be difficult to wash on account of lack of grade. Reports of yield and grade. of level are not available, but the You Bet diggings have probably produced $3,000,000. The Little York gravel area contained a fragment of the old deep channel which has been almost completely removed by hydraulic mining. (See Pl. XXIII, B.) The character of the gravel is similar to that at You Bet. As usual, the narrow, deep channel contains a hard, cemented gravel, 30 or 40 feet thick, capped by as much as 350 feet of fine gravel interstratified with some clay and sand. The bedrock elevation is 2,706 feet. Large bowlders of quartzite and quartz occur on the bedrock, both in the deep channel and on the benches. The yield has probably exceeded $1,000,000. DUTCH FLAT. The continuation of the deep channel is found at Dutch Flat, and its direction is plainly marked by the small intervening bodies of Missouri Hill and Eastman Hill. The principal area at Dutch Flat extends east and west for a mile; the gravel has a maximum depth of about 300 feet, the lower 150 feet consisting of coarse blue gravel, made up largely of metamorphic rocks, well cemented and covered by a varying thickness of finer quartz gravel, clay, and sand. (See Pl. XXI.) In the lower gravel and on the bedrock heavy bowlders are plentiful. The channel has a very strong grade, in marked contrast to the level stretch below You Bet. This is caused in part by the later tilting of the range, but in part is the natural result of the river breaking through the hard gabbro of the Serpentine belt. I[ydraulic work has been done chiefly at the eastern end at the Polar Star mine (bedrock clevation 3,075 feet) and at the western end, or Thompson Hill (bedrock elevation 2,848 fect), at both of which places the deep bedrock is exposed. At the Polar Star diggings (Pl. XCXI, B), a short distance east of Dutch Flat, some hydraulic work has been done in recent years. Little Bear Creek flows about 400 feet below the mine. The channel forms a distinct trough 200 feet wide. The bedrock is in part polished and hummocky, in part soft and decomposed. The well-cemented gravel consists of cobbles averaging at least 8 inches in diameter. It contains many bowlders, in part poorly washed; some of them are 8 or 10 feet in diameter. There is very little sand and the grade is steep, the fall being 60 feet in 600 feet to the well pit in which the gutter is exposed. About 90,000,000 cubic yards has been washed and a considerably less amount remains. Practically the whole extent of the channel has been drifted and the cemented gravel worked in stamp mills. The yield is not known but probably exceeds $3,000,000. The Polar Star hydraulic gravel is said to average 11 cents to the cubic yard.