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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  

BIDWELL BAR QUADRANGLE. 99 shows this to be composed of isotropic, translucent grains, often reddish by discoloration, and doubly refracting grains and angular particles, some of which are probably quartz. The isotropic material is probably volcanic glass. * * * The presence of the glass particles shows that these layers may represent in part volcanic ashes, perhaps from the Lassen Peak volcanic vents. The material is very light and friable. The general color of the Gopher Hill gravel is reddish, a dark red near the surface. The pebbles are usually small, from 1 to 4 inches in diameter, and by far the greater number of them are flattened. Decomposed lava pebbles were noted, but the pebbles are mostly composed of rocks of the pre-Tertiary formations, quartzite, greenstone, and siliceous argillite being represented. Pebbles of white quartz occur, but are not abundant. There is a large amount of silt and sand, perhaps one-half of the entire material. Lying about over the area that had been washed by the hydraulic method were noted many well-worn pebbles about a foot in diameter, but there were very few of these to be seen in place in the banks. A large surface of the lower gravel beds at Grub Flat and vicinity has been mined over. Underlying the wellrounded gravel northwest of Grub Flat is some decomposed ‘‘cement” gravel, made up largely of small round red, brown, and white particles, between which there has been an opaque white secondary eubstance deposited in concentric layers. Under the microscope this is seen to be a distinct tuff, but decomposed. It is made up of microlitic and glassy fragments in which the outlines of the feldspars are still to be seen. Some fragments contain fresh augite and hornblende grains, and there are also grains of serpentine present. Some of the particles are thoroughly rounded. Along Wapanse Creek some of the lake gravel is subangular. Three and a half miles east of Meadow Valley post office, on a branch of Slate Creek, at an altitude of over 4,000 feet above sea, is some gravel with angular blocks of the late doleritic basalt like that capping Clermont Hill. [Some of these gravels were formerly mined. The camp was probably the one called Hungarian Hill.—W. L.] Four miles southeast of Meadow Valley post office, on the ridge west of Deer Creek, is some Pleistocene gravel, reaching an altitude of 4,700 feet, and a gravel area west of the South Fork of Rock Creek attains an altitude of 4,500 feet. There are also gravel beds that have been mined by the hydraulic method on the ridges east and west of Whitlock Ravine. [These mines were known as Badger Hill and Shores Hill. The gravels may represent portions of a deposit formed at a former outlet of the Meadow Valley Pleistocene lake.—W. L.] These gravels are like those at Gopher Hill. There is little doubt that all of these isolated gravel patches were originally connected with the large Meadow Valley area of lake gravel, although some of them may have been formed by Pleistocene streams draining into the lake, and some of them may have attained their present altitude by displacement subsequent to the lake period. The rocky barrier between Meadow Valley and the American Valley has been cut through by Spanish Creek in late Pleistocene time, and thus the lake was drained. The production of placer gold for 1909 in the northeast corner of the quadrangle was distributed about as follows: Belden, $1,900; Bucks, $2,800; Meadow Valley, $2,100. SOUTHEASTERN PART OF THE BIDWELL BAR QUADRANGLE. Little definite information is available regarding the Neocene gravels on Mooreville Ridge and on the parallel ridges to the north. They are not extensive, nor do they seem to have been very rich, and their connection with known channel systems is very doubtful. Turner’ says: The Dodson gravel mine lies about 3} miles northwesterly from Strawberry Valley, at the south border of the basalt flow that caps the Mooreville Ridge. The gravel is from 30 to 100 feet thick, and is largely coarse, but there is fine material in places. The pebbles are of granite, andesite, basalt, quartz, and metamorphic rocks. They vary in size from small pebbles to large bowlders, all well waterworn. A considerable amount of finely preserved silicified wood is found here. Prof. Knowlton determined this as being coniferous wood (Araucariozylon). The basalt capping the mine is from 15 to 30 feet thick and shows a columnar structure in places. Some of the basalt pebbles contain crystals of chabazite in cavities. The bedrock is granite. Ludlam’s hydraulic mine is, without much doubt, on the same channel as the Dodson. It lies on the north edge of the basalt of the Mooreville Ridge, about 4 miles a little west of north from Strawberry Valley. It differs in no essential particulars from the Dodson mine. The bedrock is granite. The gravel attains a thickness of about 90 feet and the basalt capping @ thickness of about 150 feet. The lower gravel is chiefly made up of the older sedimentary and associated igneous rocks of the Auriferous slate series, and the upper part of Tertiary lavas. Fine silicified wood occurs here also. There is gravel on the Mooreville Ridge 2 miles northeast of Ludlam’s mine. Under the basalt of Kanaka Peak there are well-rounded pebbles of the kind noted at the Dodson mine. At Walker Plain there are gravel beds under the basalt. The gravel of this channel at the Buckeye House is much like that at Kanaka Peak and the Dodson mine, so far as examined. While it is not probable that all of the gravel deposits under the older basalt belong to the same period, most of them are similar in containing eome pebbles of Tertiary volcanic rocks and of the older rocks of the auriferous slate series and without doubt were formed by rivers of later age than those of the white quartz gravel period. * * * * * * * * * At the point called Clipper Mill, on the road to Strawberry Valley, is a long streak of Neocene river gravel about 600 feet wide. The pebbles are chiefly of the older siliceous rocks. There is no volcanic material associated with this area. At the west end of the andesite breccia area, or about 1}? miles cast of Clipper Mill, is a small deposit of gravel 1 Op. cit., pp. 562, 564.