The Farallon Plate
Farallon started off normally enough. It plunged beneath the North American Plate at a forty-five degree angle. This process sprouted volcanoes to form the Sierra Nevada in what is now California. Next, mantle motions pulled North America westward over Farallon, and the plate scraped along the bottom of the continent - for fifteen hundred kilometers. As North America continued its westward trek, Farallon settled to the bottom of the mantle. Crust that had accumulated above the sinking plate then bobbed up like a cork to form the Rocky Mountains.
the Rockies are fifteen hundred kilometers, or one thousand miles, to the east. The cause must be the tectonic plate that built these mountains. Its name is Farallon. Farallon was one of several oceanic plates that plunged beneath western North America and then sank into the mantle. This sinking dramatically affected the surface geology.
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NASA/Goddard Space Flight Center Scientific Visualization Studio