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.