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  

154 TERTIARY GRAVELS OF THE SIERRA NEVADA OF CALIFORNIA. . channels would have been preserved southwest of Dardanelles had the channel taken this course. The gravels exposed at Todd Valley offer no solution of the problem, for they are at a higher level and evidently represent a bench filled with gravel after the clogging of the main channel. The following solution of this problem is advanced as being most plausible: It is believed that the old channel of the Forest Hill divide emerges at Yankee Jim and Georgia Hill and trends ‘northward to Wisconsin Hill, thence through the lava ridge and curving eastward to the Morning Star mine, thence to Iowa Hill, crossing the canyon of the present North Fork of American River to Indiana Hill, and thence northward to Dutch Flat, beyond which its course has already been established. This hypothesis in the first place necessitates the existence of a deep and continuous channel between Dutch Flat and Indiana Hill. That such a deep channel exists appears now very probable and may be regarded as certain if the developments south of Dutch Flat show the existence of a deep trough at this place, which it has been asserted was found by the explorations. One of the principal difficulties appears to be the fact that the gravel at Georgia Hill and Yankee Jim differs somewhat in character from that of the Mayflower mine and Forest Hill. This may be explained by the fact that the river near Yankee Jim spread over a larger and flatter bottom, which would naturally influence the character of its deposit. The difficulty which at first glance appears to be insurmountable—that of the grades—on closer examination converts itself into an argument in favor of this hypothesis. From Dardanelles to Yankee Jim is a slight grade which is sufficient for the requirements. From Yankee Jim to Wisconsin Hill the channel would at present have a slight upward grade. From Wisconsin Hill to Iowa Hill it is apparently approximately level. From Iowa Hill to Indiana Hill it has a slight southward grade, and similarly from Indiana Hill to Dutch Flat is a grade which, though slight, is opposite to that which the river, according to this hypothesis, would have had. From Yankee Jim to Dutch Flat the Neocene river would have pursued a nearly due northerly course. Now it is likely that this river from Yankee Jim to Dutch Flat had originally a very slight grade northward, similar to that of the Neocene river between You Bet and North Columbia. Examinations of channels in other parts of the Sierra Nevada have shown the occurrence of a tilting movement which has affected the grades of the channels according to their direction. Channels running from north-northwest to south-southeast, or the reverse, have retained their original slight grade. Those running in a more westerly direction have had their grades materially increased by the tilting. On the other hand, those flowing in a more easterly direction from this axis of tilting have had their grade decreased or even reversed. A close examination of the elevations of Indiana Hill, Dutch Flat, Iowa Hill, Wisconsin Hill, and Yankee Jim will show that in fact the present levelness or slight southward grade of the channel is exactly what would have resulted if the Neocene river, with a northerly course, had participated in a westward tilting of the block of the Sierra Nevada amounting to about 60 or 70 feet to the mile. If this hypothesis is true it solves, in an exceedingly satisfactory way, a number of the perplexing problems which were presented by the enormous accumulation of gravels in the drainage of the old Yuba River. It increases vastly the drainage area of the Neocene stream, which, as now outlined, extends from the headwaters of the North Fork of the Yuba. The waters of all this territory found an outlet through the narrow channel from North San Juan to Smartsville. In the central part of this drainage area longitudinal depressions existed, . bordered on the west by the high diabase ridges of the foothills. All these conditions naturally tended greatly to increase the accumulation of gravels. What has formerly been supposed to be the North Fork of the Neocene American River now becomes the South Fork of the great Neocene Yuba River. The Neocene American River is reduced in size and consists only of the stream coming down from Pyramid Peak by way of Placerville.