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  

COLFAX QUADRANGLE. 149 this work has ceased during the last twe decades. Instead, extensive drift mining has been carried on. At the Morning Star the deep channel, extending in an easterly direction, has been mined for a distance of 3,000 feet; about 7 feet of cemented gravel is extracted, the width of the pay gravel being from 80 to 200 feet. The drift mine has proved among the richest. The gravel contained, for a long period, it is stated, $7 a carload, equal to $14 a cubic yard, and the annual production ranged from $25,000 to $150,000. The Waterhouse & Dorn or Big Dipper mine has been working the same channel from 1890 to 1902 from the Wisconsin Hill side, with excellent results. The grade of the main channel is remarkably slight, 2,692 feet being the elevation of bedrock at Wisconsin Hill, 2,685 feet at the Morning Star, and 2,631 feet at the northwest side of the Iowa Hill channel. In 1899 the workings of this mine were connected with those of the Morning Star, proving conclusively the identity of the channels. The bedrock is very uneven and hard, with many deep and often rich potholes. The gravel is coarse, with many bowlders, but is extremely well rounded. It is cemented with much granitic sand, indicating moderate grade, and is at many places noted to shingle northward. This tendency was observed long ago by J. B. Hobson in the Morning Star mine and goes to prove a northward course of the old stream. Several distinct benches, older than the deepest channel, have been mined, all of them on the east side, and up to 60 feet above the deepest trough. The gold is coarse. Along the steep east rim, high above the main channel, coarse and less well-washed gold is frequently found. A thickness of 5 or 6 feet of gravel is breasted, but the upper 3 feet usually contained but little gold. The yield in 1901 was about 135 carloads of 1 ton each in 24 hours. The average content was $6 a ton. Gravel carrying ‘less than $2 a ton was not considered to pay. The Jupiter drift mine has been worked with fair success during the last few years on a small intervolcanic channel finding its outlet on the southeast point of the Iowa Hill area of andesite tuff. The width averages 60 feet and the rims rise steeply. A smaller channel pitching into the ridge has been followed for some distance from Grizzly Flat and probably joins the Morning Star channel. A small body of well-worked quartz gravel was found at Kings Hill, 14 miles southwest of Wisconsin Hill; it is interesting because of its position between Yankee Jim and Wisconsin Hill and its comparatively low bedrock elevation (2,550 feet). Four or five acres of gravel has been washed here to a depth of 20 feet. Above Monona Flat very little gravel was exposed, the andesite tuff resting on bedrock of irregular configuration. At the Giant Gap claim, 4 miles west of Damascus, the lava cap is very narrow; below it a gorgelike intervolcanic channel has been exposed. Three miles west of Damascus is McIntyre’s claim, where a 1,000-foot tunnel has exposed the same or a similar narrow channel at an elevation of about 3,850 feet. A mile northeast of this is the Colfax claim, showing some quartz gravel (bedrock elevation 3,669 feet), probably belonging to a prevolcanic channel, the continuation of which may be found at Jimtown, three-fourths of a mile north of the reservoir. At Jimtown a shaft 100 feet deep has been sunk, finding quartz gravel and pitching bedrock. No data are available to estimate the yield of the Iowa Hill divide since 1849. It probably considerably exceeds $10,000,000. PECKHAM HILL AND TODD VALLEY. We begin now a rapid sketch of the Forest Hill divide. A small part of its area falls south of the boundary of the Colfax quadrangle. At Peckham Hill a little unsuccessful drifting has been done on the deep and narrow intervolcanic ‘‘cement’’ channel (see p. 155) finding its outlet there at an elevation of 2,183 feet. At Todd Valley is a body of bench gravel which has been washed at Pond’s claim until the overlying lava became too heavy to handle. This gravel is partly cemented, poorly washed, and about 40 feet thick. About 11,000,000 cubic yards has been washed off, the yield of which is given as $5,000,000, but this may be too high.