Black Diamond Mines Regional Preserve, near Antioch, was once the largest coal-mining complex in California. Today it offers ore of a different kind: 34 miles of trails on 3,700 acres. Our favorite hike, a six-mile loop, takes you up through oak and manzanita to high ridges and down through green valleys, past the onetime mining town of Stewartville. The old mine tunnels are mostly all sealed, but if you’re up for an Indiana Jones adventure, you can continue on to one that’s still open: the explore-it-yourself Prospect Tunnel, located three-and-a-half miles from the trailhead. Bring a flashlight—or your whip and torch—as you step 200 feet into the dank dark, hearing the echo of your footsteps, feeling the walls close in on you… Don’t worry Dr. Jones, we’re pretty sure there aren’t any rats.
Directions: From Hwy. 4 in Antioch, exit at Somersville Rd. and go south. Continue straight on Somersville Rd. (the main road goes left) into the park. The trailhead is at the end of the road. Start on the Stewartville Trail; it climbs steadily for 1/2 of a mile. Continue through a gate, then turn left onto the Ridge Trail at the T. Take the Ridge Trail for 2 miles until it ends at the Stewartville Trail. Turn right. After 1 mile, you’ll see a sign on the right for Prospect Tunnel. After visiting it, continue on the Stewartville Trail. After 1 mile, you’ll see a sign for the Miners Trail. Take this shortcut back to the Stewartville Trail, which will return you to the trailhead. *Black Diamond Mines is dog-friendly. More information.