Formation of the Sierra Nevada

The Sierra Nevada mountain range is one of the most geographically fascinating places on the face of the earth.  Although it is difficult to fathom, from 400 million to approximately 130 million years ago, an ocean used to cover the area that we now refer to as the Sierra Nevada. The formation of this glorious mountain range began with convergent plate interactions between the North American plate and the ancient Farallon plate. As the denser oceanic Farallon plate subducted beneath the North American plate during the late Paleozoic Era, the immense pressure and friction began to cause the crust of the Farallon plate to melt. As a result, plumes of plutonic rock started to float up towards the surface. The combined mass of these plutons eventually formed the Sierra Nevada batholith; with the earlier plutons forming the western half of the Sierra Nevada and the later plutons forming the eastern half. The result is one of the most spectacular granitic batholiths in the world.

According to the United States Geologic Survey, the definition of a batholith is a very large mass of intrusive (plutonic) igneous rock that forms when magma solidifies at depth. A batholith must have greater than 100 square kilometers (40 square miles) of exposed area.

The Sierra Nevada batholith was eventually emplaced during the Nevadan orogeny, a mountain building episode which occurred during the mid to late Jurassic (180-140 million years ago). Through the processes of uplifting and erosion, the batholith was, in the course of time, exposed on the surface. The resulting mountain chain has played a major role in the history of man, including being the driving force behind the California gold rush. The aforementioned immense pressure combined with mineral-rich solutions moving along cracks in the granitic batholith causes gold, copper, and other minerals to precipitate out.



Works Cited

Allen, Casey. Professor Allen’s Geog 1202 Syllabus. University of Colorado Denver, 2013. Web. 13 February 2013.

Resendes, Mary Ann. Geology of the Sierra Nevada. Central Sierra Historical Society, 2012. Web. 13 February 2013.

USGS. Geologic Glossary. US Geologic Survey Western Earth Surface Team Processes and the National Park Service, 10 February 2000. Web. 13 February 2013.

World of Earth and Science. “Batholith”. Encyclopedia.com, 2003. Web. 14 Feb. 2013.