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Yearly rainfall totals, too, change as you travel around the Bay Area. Each successive range of coastal hills blocks more and more Pacific moisture, creating a rain-shadow effect. Kentfield, in Marin County, receives about 48 inches (that’s 4 feet!) of rain per year, whereas the town of Livermore, in eastern Alameda County, gets only about 15 inches. Yet the distance between these two towns is only about 55 miles.

Climate is one thing, but daily weather is another, so it’s a good idea to check with a local source for current conditions and forecasts before heading out. You can use a weather radio, available at Radio Shack, outdoor stores, and other outlets, to receive broadcasts from the National Weather Service. You can also find up-to-the minute weather information on the Weather Channel or on the Internet at www.weather.com.

Geology

The Bay Area lies within a geological province called the Coast Ranges, a complex system of ridges and valleys that stretches from Arcata to near Santa Barbara, and inland to the edge of the Central Valley. The Coast Ranges were formed millions of years ago, as the floor of the Pacific Ocean was dragged under the western edge of North American continent. This process scraped material from the ocean floor and piled it higher and higher on the continent’s edge, in what is now California.