Mount Diablo is a lone massif towering over the eastern San Francisco Bay area, separating the valleys and ranges of the Coast Ranges from the vast Central Valley and the delta of the San Joaquin River. The high point of Contra Costa County, Mount Diablo is about 25 miles east-northeast of San Francisco. It is shaped like a volcano with two high summits (North Peak is 3557 feet) tapering down to the surrounding hills, which are all below 2000 feet. It is said that the view from the top of Mount Diablo covers 40 counties, and is the world's second most far-ranging view, after Mount Kilimanjaro of Africa. Conversely, Mount Diablo is visible from many, many places, especially on the inland side where the land is vast and flat. As a result its summit is the primary point of reference for land surveying in California, the Mount Diablo Meridian.
Mount Diablo is a popular biking, hiking, horse riding, camping, and sight-seeing destination. There is a 15 mile-long winding road that reaches the summit, where there is a visitor center building and observation deck. The paved road plays host to numerous road biking races. There are many trails criss-crossing the mountain, most are fire roads through rolling grassy terrain with open views and accessible to mountain bikes. Steeper terrain are found on the southwest (for example the sandstone outcrops at "Rock City") and northeast flanks of the mountain. North Peak (3557 feet), located 2 miles to the northeast of the main peak, is inaccessible to automobiles, and is seldom visited. It features very steep terrain with lots of rock outcrops, ideal for scrambling.
The following are the main trailheads. There are several others that are in residential neighborhoods in the surrounding towns.
1. South entrance: Take Diablo Road from Interstate 680 at the town of Danville. This is the traditional approach. Follow signs to Mount Diablo State Park. You can drive all the way to the top from here.
2. North entrance: Take Walnut Ave off Ygnacio Valley Road in the town of Walnut Creek; follow signs to Mount Diablo State Park. You can drive all the way to the top from here.
3. North - Mitchell Canyon trailhead (700 feet elevation) : Take Mitchell Canyon Road off Clayton Road in the town of Clayton, go to the end. There is a ranger station here (parking fee charged). Mitchell Canyon Road is a popular bike trail that climbs to the summit in 13 miles.
4. North - Regency Road trailhead (500 feet elevation): Take Regency Road off Marsh Creek Road in the town of Clayton, go to the end and park on the side of street (free). This trailhead accesses Donner Canyon and Back Canyon. Both canyons lead to the main peak or north peak in 6 miles through steep trails, however bicyclists can follow Donner Canyon Road for a longer ride to the summits.
5. Northeast - Marsh Creek Road trailhead (900 feet elevation): This is an unsigned, gated turn-off on Marsh Creek Road, east of the town of Clayton. Take Marsh Creek Road until it reaches its highest saddle, then park on the right. A pair of high voltage power lines crosses the road close to it. This trailhead accesses the Mt Olympia Trail, the steepest trail in the park.
Entrance fee to Mount Diablo State Park is $10 daily, collected at the North and South entrances.
Avoid summers for the oppressive heat. Spring is the best season when wild flowers carpet the grassy slopes.
Camping in designated campgrounds only. Fees and reservation required. Inquire at entrance gates.
Supposedly Mount Diablo was named by Spanish soldiers who lost a battle with local Indians in the vicinity, probably in the 18th century. The soldiers believed that the mountain was the "devil" ("diablo" in Spanish) who caused their defeat.