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  

CHAPTER 17. THE MARKLEEVILLE QUADRANGLE. GENERAL GEOLOGY. The Markleeville quadrangle adjoins the Pyramid Peak quadrangle on the east. The California-Nevada State line passes through it diagonally from Lake Tahoe on the northwest to Antelope Valley on the southeast. In California the area comprises small parts of Eldorado and Mono counties and the larger part of Alpine County. The Nevada portion lies in Douglas County. No geologic map of this quadrangle has been issued, but the main features are known from reconnaissance work by H. W. Turner in earlier years and by the writer and IH. C. Hoover in 1895. (See Pl. I, in pocket.) The southwestern part includes the eastern slope of the Sierra Nevada; along the eastern boundary extends the first of the ranges of the Great Basin, the Pine Nut Mountains, separated from the Sierra by a low pass. North of this pass, at an elevation of 5,000 feet, lies the broad and flat Carson Valley, reaching from the gentle slope of the Pine Nut Mountains on the east to the abrupt scarp of the Sierra south of Carson. South of the pass opens the Antelope Valley, drained by West Walker River, which in the extreme southeast corner of the quadrangle hugs another steep escarpment of the great range. The highest points of the Sierra, in this quadrangle, fall a little short of 11,000 feet in elevation. The western part of the quadrangle is essentially a high, glaciated ridge of granite and granodiorite, beginning on the north in the narrow buttress rising between Lake Tahoe and Carson Valley. Along the southern edge of the quadrangle granitic rocks reach across to West Walker River and form the steep escarpment west of Antelope Valley. Most of the rock is granodiorite. North of Hope Valley, extending up to Jobs Peak, the granodiorite is replaced by a normal quartz monzonite or granite similar to that which in the quadrangle to the west forms the conspicuous Pyramid Peak range. Almost everywhere the granitic rocks are jointed and fissured, in strong contrast to conditions farther down on the west slope. This jointing is especially developed in Charity Valley (Pl. VII, B, p. 32); in Summit Creek, southeast of Round Top, and in the West Carson Canyon. The most prominent joints strike north or north-northwest and dip from 40° to 80° east or west. At the Blue Lakes and Indian Valley the direction is east and west. A few small bodies of metamorphosed sedimentary rocks are embedded in the granite or granodiorite and have suffered much change from both regional and contact metamorphism. All of them present characteristics suggesting identity with the Triassic and Jurassic rocks appearing near the granite contact in the Pyramid Peak and Truckee quadrangles. One of these areas near Stevens Peak is conspicuous by the bright-red color of the outcrops and consists of black clay slates, quartzitic schists, and some limestone. The schist near Fredericksburg, at the mouth of the West Carson Canyon, is composed largely of amphibolite. A somewhat larger area of metamorphic rocks is exposed at the northern edge of the quadrangle from the Hot Springs to Genoa. The rocks are in part amphibolitic greenstones, but siliceous slates and clay slates are also present and dip west at moderate angles. The schist areas in the Pine Nut Mountains which, south of the Mountain House, extend up to the State line are somewhat different and consist chiefly of light-gray slates, in places altered to knotty schists. Highly pressed conglomerates with flat pebbles are also present. The areas exposed are not large. ° The voleanic rocks which cover the larger part of the quadrangle are divisible into two distinct series. The first comprises the main area of volcanic rocks in the center of the quadrangle with scattered patches resting on the uneven granite surface of the western part of the quadrangle. These rocks are identical with the andesitic flows and tuffs that cover so large 187