San Francisco

Environment

San Francisco is situated on a peninsula that forms the western boundary of the 1,285-square-kilometer (496-square-mile) San Francisco Bay. Its hilly terrain is part of the Coast Ranges, which extend from Oregon southward to Santa Barbara County. Among the highest peaks in the region are Mount Tamalpais (784 meters/2,571 feet) and Mount Diablo (1,173 meters/3,849 feet).

Other than its harbor, the outstanding natural feature of the Bay Area—and the one with the greatest potential to affect the lives of its residents—is the region's location on top of a network of fault lines, which has led to two major earthquakes in this century, in 1906 and 1989. The San Andreas is the best known of these tectonic faults, where portions of the earth's crust slide past each other. Normally these motions amount to an imperceptible five centimeters (two inches) per year; occasionally, however, excess pressure builds up against these plates, and when it is released, an earthquake occurs.

In 1994 the city inaugurated a 50-year plan to dispose of the millions of tons of sediment that wash into San Francisco Bay annually, threatening shipping and other activities.