Mines and Mineral Resources of Plumas County Errol MacBoyle

ISBN: 9781230234113

Published: September 12th 2013

Paperback

88 pages


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Mines and Mineral Resources of Plumas County  by  Errol MacBoyle

Mines and Mineral Resources of Plumas County by Errol MacBoyle
September 12th 2013 | Paperback | PDF, EPUB, FB2, DjVu, AUDIO, mp3, ZIP | 88 pages | ISBN: 9781230234113 | 6.26 Mb

This historic book may have numerous typos and missing text. Purchasers can usually download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1920 edition. Excerpt: ... basalt, representing anMoreThis historic book may have numerous typos and missing text. Purchasers can usually download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1920 edition. Excerpt: ... basalt, representing an intervolcanic channel later than the Tertiary gravel channels. A small patch of Tertiary gravel occurs at American House, in the Bidwell Bar quadrangle.

This deposit, lying in a sag 800 above Salt Creek, probably represents a tributary of the main La Porte channel. A capping of basalt covers the Calaveras bedrock east of the gravel patch. The bedrock to the west is amphibolite. On both east and west the bedrock rises several hundred feet, showing the old river valley. A considerable body of white quartz gravel underlies the alluvium deposit in Little Grass Valley, two miles northwest of Bald Mountain.

This has been much exploited by shallow shafts, but, being lower than the South Fork Feather River, because of excess water it can not be profitably mined. The gravel is not thoroughly rounded, thus resembling that at La Porte and Richmond Hill. Above La Porte, the channel has been seriously disturbed by movements in a fault zone which is at least one mile wide and which has a general northwest direction.

The total downthrow on the northeast side is probably 520. The first fault is exposed in the bedrock at the upper end of the La Porte diggings- here the downthrow on the east side is 55, and the gravel beds are bent over the nearly perpendicular fault scarp. Threesquarters of a mile southeast of La Porte on a bedrock of Calaveras formation a detached body of gravel lies abnormally depressed 200 below the level of the old channel. At this point the channel paralleled the fault lines, and several slices have been differentially dropped or elevated. The downthrow is 200 to the northeast, but there are several intermediate benches.

The Clay Bank tunnel, portal elevation 4000, has been driven 3000 northwest to...



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