Diablo … the "island mountain."

Sunset, April, 1985

Girdled by suburbs, Mount Diablo State Park is a unique 15,000-acre chunk of near-wilderness less than an hour from major Bay Area Freeways. Spring is the prime season to visit its now-green slopes for a picnic, a hike, or both--and enjoy the rich complexity of its natural environment. In an hour's walk, you can pass from cattle-studded grasslands to bayscented canyons where rare wildflowers briefly bloom.

On pages 122 and 123, we list walks that can introduce you to the East Bay's emerald gem this month. And we guide you to the lesser-known but wildflower-strewn canyons of the park's north side. An island surrounded by land

Rising nearly 4,000 feet above the neighboring lowlands, Diablo is an "island mountain," offering 360[deg.] views that on clear days can take in 35 counties and range for 200 miles. From its summit, you can look south, past the Livermore-Pleasanton valleys, to Mount Hamilton. On the eastern horizon, a faint calligraphic line traces the snow-capped Sierra.

Immediately northeast lie the glassy coils of the Delta. North you see Mount St. Helena, the Sutter Buttes, and, in best weather, Lassen. Nearby, in the northwest, is Mount Tamalpais, often seen cresting over a pearly surf of fog like a California gray whale curving into view. To the west lies San Francisco, laced by bridges to its hinterlands.

Because of its relative isolation, the summit is a great vantage point for surveyors; since 1851, the Mount Diablo Base and Meridian lines have been used for mapping Nevada and most of California. The varied natural environment

Many visitors do not venture beyond the view. But Diablo is much more.

It's a virtual geological museum. The core of the mountain is an ancient Franciscan plug, upthrust through 6 miles of marine sediments (mostly chert and serpentine) by pressure from the movement of two of the earth's plates against each other. A belt of sandstone envelops its foothills.

Geological diversity means diverse plant life--and, in fact, an April wildflower walk is likely to show you scores of coastal, valley, and mountain species. The northern exposures are generally richest in vegetation, except where fire has altered the landscape. In 1977, fire streaked through 6,000 acres on the north side, consuming much of the understory. You can now witness competition among shrubby plants (toyon seedlings crowd against ghostly manzanita skeletons) to regain their ground. Until shrubs fill out, wildflower displays on the unshaded slope can be stunning.

With its variety of habitats, Diablo supports an extensive food chain, and bird and animal populations are accordingly varied. Numerous non-native birds touch down, attracted by streams and forage. Natives range from the familiar California quail to such raptors as the golden eagle (look for the aerial acrobatics of its courtship behavior in early spring).

Animals include those you'd expect, plus some you wouldn't, such as the mountain lion (don't worry: it means to stay hidden). In early fall, you can even watch an exodus of hairy male tarantulas lumbering forth from their burrows, incautiously searching for mates.

The widlife census also numbers 11 kinds of snakes, all harmless except for the Pacific rattlesnake. Rattlers are most active in the morning on warm, dry days; at such times, be careful crossing rocks or fallen logs, wear ankle-high boots, and watch where you put your hands down. Hikers' paradise--especially canyons

Unlike the well-mapped trails of Mount Tamalpais, Diablo's have been created mainly by horsemen and ranchers, and so have been less publicized. That difference means a wilder environment, one with good but less-used trails that can take you through woodland, grassland, and chaparral; past seepages, streams, and seasonal falls; along lofty ridges; and up some arduously scrambled rocks.

Often, it is not a gentle landscape. Erosion-carved gullies and wind-sharpened crags give this mountain its own stark architecture. But the openness enhances its visual drama: you can always see the contours of the land, feel its presence, orient yourself. It is a land of shadow play, where the dipping shapes of birds stripe across hillsides shaded by delicate traceries of California live oak.

Dress in layers; light canyon winds can quickly bring a chill as trails twist to different exposures or higher elevations. You'll probably want the shade of a hat. Bring water. You shouldn't drink from Diablo's streams, but you can dip a bandanna in and cool your face and neck.

Some cautions: First, the North Peak, though a splendid place for views, is marred by unsightly communications towers (there's a new proposal to consolidate them and put equipment underground). Second, some trails are not yet adequately signed. Our map can get you started, but for extensive hiking without a leader, you'll want to pick up a detailed trail map ($2) at park headquarters. Third, watch out for poison oak.

Some of the most appealing trails--uncrowded, floriferous, and shady--are in the park's north canyons (see you map). To reach these, you need not use park roads but can exit Ygnacio Valley Road (reach it from either State 24 or Interstate 680) southeast on Clayton Road. Turn south on Mitchell Canyon Road to the Mitchell Canyon trailhead. For Donner and Back canyons, park at the end of Regency Drive (past Clayton's small downtown). Clayton: still a staging point