Along the northeastern shore of the Great Ocean, a long, thin strip of land stretches 1500 miles, in about as straight a line as Nature will allow Herself to draw. The strip is born of the grinding of the great oceanic plate against the continental plate.

From Cabo San Lucas to Cape Mendocino, California is characterized by a system of strike-slip faults between the Pacific and North American plates, but California is more than a mere side-swipe; it is a collision, and this intercontinental collision involves—like so many others—one continent wedging under the other. In this head-on component of the collision vector is born the Sierra Nevada.

The uplift of the Sierra Nevada has not been gentle. It was associated with one of the most powerful earthquakes in California history, the Great Lone Pine Earthquake. It has also been associated with one of the most fantastic volcanic events known to science: the Long Valley supervolcano.