The Mt. Diablo Summit Trail starts from South Gate Road right as it leaves the residential area. Take Highway 680 to Diablo Blvd. in Danville and head east for 3 miles. Turn left onto Mt. Diablo Scenic Blvd. at the stop sign. Drive for a mile until you get to the park boundary. This is marked by a gate and speedbump. There is a dirt strip on the right side of the road to park. Directly across the road is the trailhead.
The trail starts out as a single track for about 3/4 of a mile where it crosses a bridge. Turn right onto the fireroad here (uphill). At about the 1.5 mile mark you come out onto a pave road. Turn left and find the trail down the road 50 yards or so. Follow the single track through the trees until you come out on a fire road. Turn right and then shortly after take a left onto another single track. This will take you up a steep section to another fire road on a ridge that parallels the road. From here you keep following the fireroad. After crossing the road twice, there is a ranger's house on your left. Hike past this and continue up. You will cross the road a few more times before joining the summit loop, where you can go right for a hike around the summit, or left for the shortest route to the summit. You cross the road once more where you take the trail in the middle of the two directions of the road. Soon you're at the summit museum and lookout. If you want some short, easy rockclimbing, go to Devil's Pulpit, which is the brown rock outcropping to the SE of the summit. You can get there on the summit loop trail. The trail is usually well signed and if in doubt, go up. This route is about 5.5 miles one way with 3,000 ft. net gain or 3,300 ft. total gain. It can also be mountain biked legally until Rock City, although it is a fireroad almost all the way to the top.
Water, which can be filled at Rock City and the Summit, layers (always a lot colder on top), and anything else you'd bring on a moderate day hike. You can bring some climbing gear if you want to go to the bigger rocks at Rock City.
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