A popular spring/winter training hike for those in the Bay Area, this tour of the northern half of Mt. Diablo State Park takes in four of the park's prominent high points: Eagle Peak, Mt. Diablo, North Peak, and Mt. Olympia. It features gorgeous wildflowers in the spring, superb views, and even a little optional scrambling. With an abundance of trails and fire roads in the park, the route is subject to many variations depending on how long a day one wishes to enjoy; the variation below is roughly 13-14 miles or so. The total elevation gain for the loop described below (including Falls Trail) is on the order of 5000 feet or so.
Start from the Mitchell Canyon trailhead, elevation 640 ft, located at the end of Mitchell Canyon Road
in Clayton. A small information centre is usually staffed in the trailhead parking area, where you can purchase maps of the park; these are highly recommended given the enormous number of fire roads and trails here.
The park doesn't open until 8am, and there is no parking along the road for the last mile before the entrance - the first legal parking outside is at a sign noting "Not a through road" on the right side as you drive in. If you wish to get an early start, this will add another mile or two onto your "approach."
From the Mitchell Canyon trailhead, follow the Mitchell Rock trail as it winds its way up the wooded hillside over Twin Peaks until it reaches a junction with the Eagle Peak trail; wildflowers can be abundant in this section during the spring. Continue right from this trail junction through open terrain over Eagle Peak (2349 ft; a small unsigned spur trail leads over the actual summit). From here, the trail drops down about 400 ft before climbing again to Murchio Gap (2320 ft). From the gap, continue along the Bald Ridge trail to reach a fire road and informational plaque at Prospectors Gap (2960 ft).
From Prospectors Gap, turn right on the North Peak trail. Along the way, you'll notice several rock outcroppings to your right, amongst which is Devil's Pulpit. For those looking for a slightly more direct--and enjoyable--route to the main summit, a well-worn use trail leads up the hillside through some of these rocks, eventually leading to a maintained interpretive trail alongside Devil's Pulpit. This variation is (contrived) class 2-3 on excellent rock. Devil's Pulpit itself is a very short class 2 scramble from the east, and probably class 3 if approaching from the west (i.e. the main summit).
From the main summit, retrace your steps to Prospectors Gap, and follow the North Peak Road steeply up to North Peak (3557 ft). From North Peak, there are a couple of options. The easiest is to make your way down to the North Peak trail, which leads to Mt. Olympia
(2946 ft). A harder option follows the ridgeline directly to Mt. Olympia; this variation features some extremely
loose class 3 rock and a bushwhack through poison oak. I don't recommend this.
From Mt. Olympia, it's mostly downhill the rest of the way as you make your way back down via the Mt. Olympia Road/Mt. Olympia Trail, Tick Wood Trail, Back Creek Trail, and Coulter Pine Trails. Any number of variations are possible here; one recommended choice is to take the Falls Trail around for some superb views of Mt. Olympia and North Peak.
None, but bring plenty of water; it can get hot out here with not much in the way of shade, and there's little water found along the route. Be sure to refill your water bottle at the main summit; the next water isn't until you reach Donner or Back Creek, by which time you're likely just coasting downhill.