Geology of the Sierra Nevada Mountain Range By

Geology of the Sierra Nevada Mountain Range By Elena Kurbatova South Lake in the Sierra Nevada Mountains, courtesy of Duane Shoffner

Geological History Late Jurassic, Cretaceous, and Tertiary Periods • Kula and Farallon plates are subducted under the North American plate. • Hot felsic magma coming from the mantle starts rising, producing a chain of volcanoes on the continent. • Volcanic eruptions produce layers of solidified magma, most of which stays deep below the surface and forms plutons of solid granite.

Subduction of the Farallon Plate beneath the North American continental margin, 140 -100 million years ago.

Late Cretaceous Period • Plutons come together to form the single, massive batholith (deeply imbedded rock). • Batholith begins to rise. • The layer of marine sedimentary rock that lay over the mountain is gradually eroded away and deposited in the valley. • The granitic core of the range is exposed.

Granite is exposed

Tertiary Period • The continental crust east of the Sierra Nevada begins to stretch in an east-west direction. • The crust breaks into a series of north-southtrending valleys and mountain ranges—the beginning of the Basin and Range province. • The Sierra Nevada Range starts rising along its eastern margin.

What might have caused the uplift: • The oceanic plates are subducted and become completely overridden. • The North American and Pacific plates come into direct contact for the first time. • Shear replaces compression as the North American plate begins interacting with the Pacific plate. • On the other side of the Sierra Nevada Range Basin and Range Province is being pulled apart.

Faulting

The Sierra Nevada Faults • The Sierra Nevada Fault is a normal fault produced by tension • There is also a smaller strike-slip fault produced by shearing stress

The Sierra Nevada is an enormous tilted fault block

Quaternary Period • Not long after the Sierra uplift begins, the Earth cools. • Glaciers grow in the Sierra highlands and make their way down former stream channels, carving U-shaped valleys. • The combination of river and glacier erosion exposes the granitic plutons previously buried, leaving only a remnant of metamorphic rock on top of some of the Sierra peaks.

What makes the Sierra Nevada Range geologically interesting • Gold deposits in the foothill metamorphic belt • A possibility of a major earthquake along the fault line • The unpredictability of the future plate movement

Web sites consulted Sierra Nevada Physical Geography Joel Michaelsen http: //www. geog. ucsb. edu/~joel/g 148_f 09/readings/sierra_nevada. html • Sierra Nevada Mountains (Geology) http: //www. knowledgerush. com/kr/encyclopedia/Sierra_Nevada_Mountains/ • America's Volcanic Past Sierra Nevadas http: //vulcan. wr. usgs. gov/Living. With/Volcanic. Past/Places/volcanic_past_sierra_nevadas. ht ml • Pacific Mountain System http: //www. nature. nps. gov/Geology/usgsnps/province/pacifmt. html • GEOLOGY OF THE SIERRA NEVADAS Mary Ann Resendes http: //www. sierrahistorical. org/archives/geology. html • Geology of Yosemite http: //www. nps. gov/yose/naturescience/geology. htm • California Geological History snobear. colorado. edu/. . . /California. Mtns/California_geologic_history. pp •