Sierra Nevada

The earliest granite was formed in the Triassic period. Toward the end of that period, and into the Jurassic period, the Nevadan orogeny occurred. Later, during the Cretaceous period, the subduction of the ancient Farallon Plate caused magma to rise, creating the Sierra Nevada batholith. A mere 32 to 50 million years later, this 'proto-range' became eroded down to low rolling mountains, just a few thousand feet high. Then, about twenty million years ago, extensive volcanismoccurred. About four million years ago, the range as we know it began to form when a large block of the Earth's crust began to tilt toward the west. Deep canyons began to be cut on both sides of the range by the erosive action of rivers. The overall climate of the Earth began to cool, and ice ages began, around 2.5 million years ago. Glaciers cut away the classic U-shaped canyons throughout the range. River and glacier erosion subsequently exposed the remnant of metamorphic rock that remains atop some of the peaks today. Uplift continues, causing large earthquakes.

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