Plumes of liquid plutonic rock known as plutons joined together and began to rise above the earth's surface resulting in the formation of the Sierra Nevada 20 million years ago. The oldest sections of the Sierra Nevada are located in its western half, while its eastern half was formed only 10 million years ago.
Until 130 million years ago, the area that is now the Sierra Nevada was entirely covered by the ocean. Its formation, however, had already begun. Almost 250 million years ago, during the late Paleozoic period, friction caused by the movement of tectonic plates under the ocean floor resulted in the melting of the Pacific plate. The plumes of plutons that formed the Sierra Nevada occurred as a result of the melting of the Pacific plate. These plutons began to rise above the earth's surface 80 million years ago.
The Sierra Nevada foothills are composed of Table Mountains, formed from ribbons of hardened lava from volcanic explosion. Lava from volcanic eruptions over time, as well as glaciers help give the Sierra Nevada its shape.
The Sierra Nevada is around 70 miles wide and stretches 400 miles north to south. The Sierra Nevada is located primarily in California, with the exception of its Carson Range, which is located in Nevada.