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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  

CHICO QUADRANGLE. 85 less altered diabases, basalts, or augite andesites—which form ridges trending north-northwest and as a rule rise abruptly from the rolling foothills covered with Quaternary gravels. Browns Valley Ridge, north of Yuba River, in the Smartsville quadrangle, is one of the best instances of this tendency. At Oroville and north of it the greenstone ridges also rise sharply from the sediments of the valley, but their direction changes here to more nearly north. North of Cherokee the principal ridge follows the east side of West Branch up toward Magalia, rising to a height of a thousand feet above the gently sloping tuff plateau on the west side of that stream. The same conditions, more or less pronounced, continue northward to Inskip and Chaparral, the latter situated in the Lassen Peak quadrangle. The bedrock ridge here rises to elevations of over 5,000 feet, and the Tuscan tuff spreads westward about 1,000 feet lower. North of this point the lavas of the Lassen Peak quadrangle cover everything, the contact line between the bedrock and the lava fields turns eastward, and the conditions become complicated by the appearance of late Tertiary or Quaternary faulting. This sharp slope was even more pronounced in Neocene time than at present. At Smartsville the Neocene Yuba River broke through the greenstone barrier, which rose a thousand feet above the stream. At Oroville, where the present river has cut through the ridge and exposed the Neocene surface on the north side, the slope of this surface close to the valley is 1,000 feet in a little more than 3 miles. Between Cherokee and Pentz the escarpment is very well marked, and the section from Magalia to Sawmill Peak (Pl. XV; fig. 7, p. 93) shows a rapid rise of 1,500 feet of the Neocene surface. West of Magalia, as shown by the exposures in Butte Creek, the slope is less steep, but the bedrock soon disappears underneath the lavas. In the area here described there existed no master stream like the Neocene Yuba River, which debouched near Smartsville. Doubtless many smaller streams drained the area, but the Neocene headwaters of the Yuba included the upper reaches of the present Feather River. The range, north of the Yuba, was in Neocene time an elevated region with many ridges trending northwesterly and northerly. The great flows of andesite tuff which followed down Yuba River to the Sacramento Valley failed to cover these rolling uplands and no connected areas of these volcanic flows are to be found below the western foot of the escarpment north of Cherokee. The Neocene gravels of these uplands were easily destroyed by later erosion. The present Table Mountain north of Oroville is the remnant of a flow which evidently originated in the foothills of the range. There was, as stated above, no Neocene river corresponding to the present Feather. One of the numerous smaller streams taking its place was that whose gravels have been mined so successfully at Cherokee, 10 miles north of Oroville. Neocene shore gravels appear along a north-northwestward-trending line from Cherokee to Mineral Slide and Helltown, on Big Butte Creek. The northeastern part of the Chico quadrangle was drained by a very well defined channel deeply cut through the greenstone ridge. Its upstream course runs from the Mammoth shaft, 2 miles west of Magalia, to the Parry incline, 3 miles north of the same place, and thence up below heavy covering volcanic masses to the northeast corner of the quadrangle. (See Pl. XIV.) West of this deep channel are a number of small but rich channels draining westward across the present canyon of Big Butte Creek, north of Nimshew. The Neocene gravel deposits of the Chico quadrangle have been described as shore gravels by H. W. Turner,' but except for certain deposits near I[elltown and Mineral Slide, on lower Big Butte Creek, such.a view seems untenable. Everything indicates, on the contrary, a rough configuration of the Neocene surface and a steep slope from the highlands of the Bidwell Bar quadrangle and the eastern part of the Chico quadrangle to the lower country covered by the Tuscan tuff. Shore gravels may well exist under the covering lavas through the ‘‘Lassen Straits’? of Diller, supposed to connect the Sacramento Valley with the Neocene lakes of the Great Basin. However, the most northerly exposure of the bedrock formation of Deer Creek, in the southwestern part of the Lassen Peak quadrangle, shows plainly that a deeply eroded stream bed existed here, partly filled with auriferous gravel? 1 Op. eit., pp. 545, 546. 2 Diller, J. S., Geology of the Lassen Peak district: Eighth Ann. Rept. U. S. Geological Survey, pt. 1, 1889, p. 416.