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  

84 TERTIARY GRAVELS OF THE SIERRA NEVADA OF CALIFORNIA. The pre-Tertiary erosion emphasized the longitudinal structure, and this found expression in the courses of the ancient streams. The range had a much lower elevation than at present. Along the western margin the most prominent feature consisted in the abrupt greenstone ridges which from Mariposa County to Butte County followed the valley line. West of these ridges was a series of depressions which rose toward the east into an undulating plateau, and this was surmounted by a much higher ridge of flat-topped hills. In general the rivers broke through the greenstone ridges of the foothills in deep and rocky narrow valleys, but east of these ridges followed the central depression for longer or shorter distances. Farther upstream they again bent to the east, and their sources lay in the highest ridge of the Tertiary range. From north to south, principal streams described below have been recognized on the western slope. (See Pl. I, in pocket; fig. 3, p. 40.) Magalia channel.—A minor watercourse, which may be termed Magalia River, had its source in the northwestern part of the Bidwell Bar quadrangle and its outlet near Centerville, a few miles northeast of Chico. It flowed in a narrow canyon-like valley, rapidly widening at Centerville, where also large masses of gravel began to accumulate. Where exposed by mining operations near Magalia the channel was found to be filled with large bowlders and coarse sand, but the total depth of the prevolcanic deposits is probably not more than 50 or 75 feet. Stream near Cherokee—A somewhat similar but shorter stream is well exposed near the valley border at Cherokee. It shows the same characteristic of coarse, heavy: bowlders resting in a well-defined though not V-shaped depression. The depth of this coarse gravel is 35 feet, and above it lies about 250 feet of sand and clay of the Ione formation. Yuba River.—The Tertiary Yuba River was the largest of the streams draining the western slope. Its headwaters extended from the southern part of Plumas County southward to the dividing line between Placer and Eldorado counties on upper Rubicon River, a distance of about 60 miles. Its outlet, like that of its present equivalent, was near Smartsville, in Yuba County, at the valley border. Its course from North San Juan to Smartsville was southwestward for 20 miles; in this distance the united branches of the river broke through the greenstone ridges of the foothills in a valley, which, as can be seen at Smartsville and French Corral, had a depth of more than 1,000 feet. At Smartsville the bed of the Tertiary river was 200 feet above the present Yuba; at North San Juan about 700 feet. Coarse gravels to a depth of 170 feet filled this old trough and they are directly overlain by andesitic gravels and tuffs. Between French Corral and North San Juan the average thickness of the gravels was probably 200 feet. Above North San Juan the river began to branch. An important tributary came down from the vicinity of Gibsonville, in Sierra County, by way of Camptonville. Heavy gravels of prevolcanic age are also present along this branch. At Poverty Hill the trough is filled to a depth of 25 feet with coarse gravel.and large bowlders, above which lies a wide body of fine quartz gravel up to 120 feet in thickness. At La Porte the gravels are 130 feet thick and in the upper part consist of fine quartz gravels, in places mixed with thick beds of clay. Throughout the distance from La Porte to Smartsville the direction is southwest and the grade averages 100 feet per mile, though above La Porte it locally increases to 170 feet. The headwaters of the northern branch can not be traced to their sources, for at Gibsonville the channel is cut off by the canyon of the South Fork of Feather River, beyond which dislocations make further tracing impossible. Moreover, this locality is near a volcanic region whose eruptions have disturbed the old stream beds. From North San Juan, or a short distance east of it, the trend of the river going upstream turned abruptly to the southeast and for 25 or 30 miles followed a longitudinal depression parallel to the crest of the range; this direction continued as far south as Forest Hill. In this old depression the heaviest gravels found within the range have accumulated. They were contributed by numerous streams from the east and apparently held back as if by a dam by the narrow canyon of the lower, transverse river course. At North Columbia the depth along the center of the channel is from 400 to 500 feet. The gravel in the deepest trough is coarse and in places bowldery, but the top gravels spread out over the benches are fine and more quartzose. At North Bloomfield, on a tributary that joined the main river at North Columbia, the deepest