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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  

TOPOGRAPHY AND GENERAL GEOLOGY. 39 the Pyramid Peak Range in a deep canyon. Its headwaters extended much farther east and are probably to be found at some place in Alpine County, in the Markleeville quadrangle. To the west of this old divide a number of flat-topped mountains rise to elevations of about 6,000 feet; prominent among these are Robbs Peak, in Eldorado County; Canada Hill, Bald Mountain, or Duncan Peak, in Placer County; and several others. Most of these peaks consist of harder masses of metamorphic slate which have resisted erosion better than the granodiorite. All these level-topped peaks and ridges, rising prominently above the general surface of Tertiary time, undoubtedly indicate a far older eroded surface, uplifted and dissected long before the auriferous gravels were deposited or the lava flows extruded. The important fact that the Tertiary rivers cut back behind this pre-Tertiary divide and robbed the streams to the east of it indicates that the eastern slope at one time had a slighter grade than the western; in other words, the western streams were superior in eroding power. The exact age of this ancient topographic surface is difficult to ascertain. It assuredly antedated the Eocene and it may be early Cretaceous. The line of high peaks indicated above is believed to represent the crest line of the Sierra Nevada in Cretaceous time. (See Pl. XVIII, . 134.) P EASTERN FAULT SYSTEM. OUTLINE OF SYSTEM. The great fault which delimits the Sierra Nevada from the Great Basin on the east has attracted the attention of every geologist who has studied the range. It finds expression in an imposing scarp which can be followed from a point about 40 miles south of Owens Lake, in latitude 35° 30’, to Honey Lake, in latitude 40° 20’, a total distance of 350 miles. (See fig. 3.) When studied in detail it proves to be a complicated fault system produced by a number of successive movements. The south end of the fault line bends sharply to the west and gradually loses itself toward Tehachapi Pass. North of Honey Lake the fault is covered by heavy masses of Quaternary lava. The fault scarp is most imposing south of Owens Lake, where it descends abruptly from elevations of 11,000 feet to 3,569 feet. From Owens Lake the fault scarp can be followed almost continuously to Mono Lake, which also lies at its immediate foot. From Mono Lake northward instead of a single fault there is a system of dislocations, spreading out northward, each dislocation being usually offset from the next by a few miles, en échelon. The main fault continues only for about 50 miles northwest of Mono Lake and is still apparent by its steep escarpment on the west side of West Walker River near the California-Nevada boundary line. About 10 miles to the north of Markleeville begins another fault line which extends northward in Nevada to a point a few miles south of Reno. Another offset of a few miles probably exists here, although the covering Tertiary andesites veil much of the structure. From a point about 10 miles west of Reno, near the State line, an escarpment indicating a fault extends at first in a northerly direction, but with some irregularities which indicate the existence of several parallel faults. From Long Valley to a point near Susanville the extremely well marked fault scarp runs in a northwesterly direction but within a short distance diminishes in height and becomes covered by lavas. From Lake Tahoe northward a series of gradually diverging faults extend toward Plumas County. The first is indicated by the eastern shore of Lake Tahoe but dies out a short distance south of the Lake. To the north it continues with a slight offset at the north end of the lake and forms a westward-facing escarpment extending in all 70 miles northward to the east side of Sierra Valley. A similar fault, but with a scarp facing eastward, begins a few miles south of Lake Tahoe and continues northward along the west side of the lake though locally obscured by heavy masses of andesites. This fault line skirts the southwest side of Sierra Valley and here bends more sharply to the northwest. It has been identified along the west side of Mohawk Valley and is probably continued to the northwest as far as Quincy. A third fault line, not so conspicuous as the one just mentioned, lies about 18 miles to the southwest of Mohawk Valley; it begins near La Porte and continues for 20 miles to the northwest. An intermediate disturbance