Week 5- Converging Plates: Sierra Nevada
(Bethsaida Colina)

Sierra Escarpment viewed from the east. In the foreground is Tinemaha Reservoir in the Owens Valley.

Personally,  I have seen this beautiful nature many times because I used to live in this part of the country. Sierra Nevada, also called Sierra Nevadas, major mountain range of western North America, running along the eastern edge of the U.S. state of California. Its great mass lies between the large Central Valley depression to the west and the Basin and Range Province to the east. Extending more than 250 miles (400 kilometers) northward from the Mojave Desert to the Cascade Range of northern California and Oregon, the Sierra Nevada varies from about 80 miles wide at Lake Tahoe to about 50 miles wide in the south. Sierra Nevada margin oceanic crust against continental crust. The mountains formed during a period of concentrated plate tectonic activity that shaped much of the jagged landscape of the western United States.  The Sierra Nevada in California is a fault-block mountain range. The range moved up along a normal fault along its eastern edge. The block on the other side of the fault dropped down. This combination of upward and downward movement formed the steep eastern side of the Sierra Nevada. The western side of the range tilts down gently toward California’s Central Valley.  Therefore, it is formed by both folded mountains and fault-block mountains form over millions of years. 

Position of Sierra Nevada inside California

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.

According to the U.S. Geological Survey, the region of the Sierra Nevada Mountains provides evidence of ongoing mountain building, which means that the shape and movement of these mountains are influenced by the shifting of tectonic plates beneath the earth's surface. Because of all this shifting, this region is also peppered with volcanoes. The most impressive, Mt. Shasta, rises 14,180 feet above sea level in the Cascade Range, about 80 miles south of the Oregon border. The Sierras host the tallest peak in the continental United States -- Mt Whitney (elevation 14,505 feet). It is less than 100 miles west of Death Valley, the lowest point in North America.

Mount Whitney, the highest peak in the range and the contiguous United States

The Sierra Nevada Mountains are comprised mostly of granite that was formed from the lava of volcanoes. This mountain range is considered young because it started to emerge from the earth due to the erosion of the volcanic rock only about 5 to 20 million years ago.

References: 

Armand J. Eardley John W. James. (2019, February 21) Sierra Nevada. Retrieved from: 

https://www.britannica.com/place/Sierra-Nevada-mountains

Geology & National Parks. USGS. Retrieved from: 

https://geomaps.wr.usgs.gov/parks/province/pacifmt.html

Mary Ann R. (2012, March 5) Geology of the Sierra Nevada. Retrieved from: 

http://www.sierrahistorical.org/geology-of-the-sierra-nevada/