Why California's coast fell into the ocean.

Southern California's coastline fell into the ocean 20,000,000 years ago as a result of one of the biggest land mass movements known in geology, according to Louisiana State University geologist Roy K. Dokka, who has been studying the Mojave Desert for the past 20 years. It was the Trans Mojave-Sierran shear zone, a giant fault zone that few knew existed or paid little attention to before now, which pulled the trigger that moved 500,000 square miles of land 60 miles over a period of 2,000,000 years.

The interconnected system of faults defines the boundaries of a huge continental fragment--bigger than all of New England--that detached from the North American plate and moved toward the Pacific. The severed area involves a land mass roughly 400-by-800 miles, extending from the Mojave Desert to Tucson, Ariz., to Sonora, Mexico. The coastal edge of this fragment was "sawed off" and subjected to the northwest movement of the adjoining Pacific plate.

"Imagine the force that moved this gigantic land mass--as much as 60 miles deep--60 miles to the southwest at the breakneck speed of about four inches a year. That's about twice as fast as what fingernails grow. To geologists, that's pretty fast....

"In the process, the continental...