Afoot and Afield: San Francisco Bay Area. David Weintraub

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      Hikers take a break just off Pine Mountain Road, with Mt. Tamalpais in the background.

      Bay Area parklands are administered by various federal, state, and local agencies, listed in Appendix 3.

Climate

      The Bay Area’s climate is perfect for outdoor activities, with a dry season that lasts from May through October and a generally mild, if damp, winter. In summer, expect fog and cool temperatures near the coast, thanks to Pacific Ocean. Inland, temperatures can soar. The generally clear days of autumn are fine for hiking just about anywhere. The first rains turn hillsides green and fill seasonal creeks.

      Winter storms from the Gulf of Alaska can drench the Bay Area and even bring snow to the highest peaks. Cold, clear weather usually follows—a great time to bundle up and visit high-elevation vantage points. Spring can be sunny, rainy, tranquil, or blustery—or a combination, sometimes on the same day! This is when the Bay Area’s grasslands come alive with colorful displays of wildflowers.

      The Pacific’s moderating influence diminishes as you go inland. Temperature differences—the spread between the average highs and lows for any given location—widen as you leave the coast. Here’s an example: The highest average high temperature for San Francisco is 68.5°F, whereas the same figure for St. Helena in Napa County—only about 65 miles away—is 89.2°F. But San Francisco’s lowest average minimum, 45.7°F (January), is about 10°F warmer than St. Helena’s.

      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.

      Within the Bay Area are sub-ranges such as the Sonoma, Mayacmas, and Vaca mountains in the North Bay; the Diablo Range in the East Bay and South Bay; and the Santa Cruz Mountains on the Peninsula and in the South Bay. The tallest peak in the North Bay is Mt. St. Helena (4343’), at the corner of Sonoma, Napa, and Lake counties. Other prominent Bay Area summits include Mt. Hamilton (4213’), Mt. Diablo (3849’), Loma Prieta (3806’), Mt. Tamalpais (2571’), and Sonoma Mountain (2295’).

      Olcott Lake in Jepson Prairie Preserve, a seasonal pool, hosts a variety of plants and animals, some quite rare.

      Most of the surface rock in the Bay Area is sedimentary, but volcanic activity has occurred here in the past. Young volcanic rock caps the Mayacmas and Vaca mountains bordering the Napa Valley, and there are four extinct volcanoes in the East Bay, including Round Top (1763’). California’s state rock is serpentine (more properly, serpentinite), gray-green in color and often seen as outcrops beside the trail. Serpentine forms a soil that is toxic to many plant species, but some have adapted to it. Among these are Sargent cypress, leather oak, and a variety of uncommon wildflowers.

      The San Andreas fault—which splits the Santa Cruz mountains and slices through Marin County—and a host of lesser faults crisscross the Bay Area. As the Pacific plate slides past the North American plate, tremendous bursts of energy are sometimes released in the form of earthquakes. Most of the time, however, the northward movement, which, over the last 25 million years has carried granite from southern California to Point Reyes, is imperceptible. Visit Point Reyes National Seashore in the North Bay, Sibley Volcanic Regional Preserve and Mt. Diablo State Park in the East Bay, and Los Trancos Open Space Preserve on the Peninsula to learn more about Bay Area geology.

      Little Yosemite is a rocky gorge on Alameda Creek, perfect for picknicking and nature study.

Plants

      California has a rich diversity of plant life. Some species, like coast redwoods, date back to the dinosaurs, whereas others have evolved within the past several thousand years. Roughly 30 percent of the state’s native plants grow nowhere else. These endemics, as they are called, include many types of manzanita (Arctostaphylos) and monkeyflower (Mimulus). Botanists divide the plant kingdom into several major groups: flowering plants, conifers, ferns and their allies, mosses, and algae. A plant community consists of species growing together in a distinct habitat. Here are the principal plant communities you will encounter along the trails.

      OAK WOODLAND

      Inland from San Francisco Bay, the fog-free hills between 300 and 3500 feet host a generally open woodland, sometimes called a savanna. Species here include various oaks, California buckeye, gray pine, California bay, buckbrush, toyon, coffeeberry, snowberry, and СКАЧАТЬ