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It was awhile back, but the whole central valley used to be a lake. Previous to that, much of the northern half of California was covered in lava. Pretty interesting geologic history in these part.

A little further north, Yellowstone is a hot spot that hopped east across the north American plate, leaving calderas from the pacific to its current location. The Yellowstone resivor is cut off, and the hot spot is moving on to the east now. (no more supervolcano eruption possible there)