Two great plates, the Pacific and the North American, meet in California. The Pacific Plate is moving north, creating a transform fault (the San Andreas and related faults) Over the last 20 million years the Pacific Plate has slid about 200 miles north. If it keeps moving as predicted, San Francisco will become neighbors with Seattle in 20 million years!

Because the San Andreas fault curves around Los Angeles, and then again into the Pacific in northern California, the two plates cannot slide smoothly against each other. Instead, the complex stresses of plate movement have fractured the land and created dozens of smaller fault lines. The Hayward fault in the Bay Area and the Newport - Inglewood and San Jacinto faults in southern California are two of these smaller faults that pose as great a threat as the San Andreas.

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