The following description was written by Phil Stuecheli (email@example.com):
Mt Diablo is located between Walnut Creek and Concord in central Contra Costa County. Access it via HWY 680 to Ygnacio Valley Road to various trailheads (see a map), or from Stone Valley Road to Macedo Ranch (again consult trusty map).
My favorite ride starts at the Mitchell Canyon Trailhead, at the end of Mitchell Canyon Road. To get there take the Ygnacio Valley exit off HWY 680 north, in Walnut Creek. Follow Ygnacio east, through Concord to Clayton Road. Turn right on Clayton Road, and proceed to Mitchell Canyon Road, where you turn right. Follow to the end of the road and park, either in the Mt Diablo State Park lot ($2.00 fee), or park on the road.
The trailhead starts at the parking lot at an elevation of about 600 feet (water is available). The trail is a fire road, passing up Mitchell Canyon, along Mt. Diablo Creek. The first 2 miles are a gradual climb, a nice warmup. After that the fun starts! The next mile climbs relentlessly for 1,000 feet up a series of tight switchbacks to Deer Flat. At Deer Flat, take the right-hand fork, (Deer Flat Road). After a brief reprieve, the climb begins anew, as you ascend 800 more feet to Juniper Campground. Proceed through the campground (there is water here) to the main park road. Turn left, and take the pavement for about a mile to a 180-degree hairpin (Devils Elbow). This is the high point of the ride, at 3,500 feet. There is a gravel turnout at this point that is the beginning of the (legal) North Peak singletrack. The trail is a moderately to highly technical rocky, (loose during late summer) beautiful singletrack that descends about 550 feet in about three-quarters of a mile. Be sure to take in the spectacular views of the Sierra Nevada and Central Valley on the way. At the base of the trail, take the steep Prospectors Gap Road north (hard left). This fire road is VERY steep and rocky, so watch out. You descend 800 feet in short order looking out on your right for the Meridian Ridge fire road. Turn right, and descend a screamingly fast, straight, rolling ridgecrest road, looking out for the sharp right turn in the road. Descend to the Donner Canyon trail (fire road), and turn left (north). The road follows Donner Creek to an intersection where you turn left out of the canyon, and across relatively flat topography to the Mitchell Canyon parking lot at the trailhead.
Total distance is about 13.5 miles, with about 3,000 feet of climb. The ride usually takes me about 2.5 hours, at a good pace. The best times are in the spring and fall, since Mitchell Canyon is hellishly hot in the summer. In the winter, you will want to avoid a stretch of sticky adobe soil on the lower part of the return loop by skipping the Meridian Ridge descent, and continuing straight (west) along the Prospectors Gap road, up a short climb to the saddle at Murchio Gap, and down another steep section of gravely road that will take you back to Deer Flat (be prepared to ford a deep puddled in late winter). From there, turn right and down, returning down the Mitchell Canyon road to the starting point. In general, the soil conditions on the upper parts of Mt. Diablo are excellent for winter riding, with most roads cut into hard igneous and metamorphic rocks that form a good all-weather surface. Getting past the muddy lower reaches is best accomplished by starting at the Mitchell Canyon trailhead (only a short muddy section), or by driving partway up on the pavement. There are now no cows on the mountain, and the wildflowers are truly spectacular in the spring. The Park sells an excellent map, on a USGS contour base, with accurate trail mapping. The map is widely available at local bike shops and REI.
©1995-2007 Ross Finlayson