Hike through old mining country
Black Diamond Mines Regional Preserve is a 6,000-acre park in the East Bay Regional Parks District, and has some excellent hiking. The deep canyons harbor California buckeye, live oak and dense shrubbery. Grass that ranges from gold to green cloaks the high ridges along with nice stands of Coulter and gray pines. The old townsites, mines and cemetary are an added bonus.
Walk south/uphill from the parking lot for .13 mile on a paved road then go left on the Nortonville Trail. Nortonville heads uphill to the west next to an orchard. The Somersville Townsite is to the north on the other side of the drainage from the first 0.4 mile stretch of Nortonville. Nothing remains of the old town except for flat ground. There's also an interesting stretch of black ground that's the result of prescribed burns rather than the coal that once made this area a mining hotspot.
The so-called Black Diamond mines operated from the 1850s to the early 1900s, and there are numerous reminders. After a modest climb you'll reach the turnoff to the Rose Hill Cemetery. It's worth checking out because of the ongoing restoration. The EBRPD even has a kiosk with pretty nice brochures that detail known grave sites and eulogizes a few prominent individuals. Many tombstones date back 140+ years.
Head back to the Nortonville Trail as it climbs another .10 mile to a small saddle. A grass-covered mountain rises sharply to the north (with an interesting looking unofficial trail climbing up its spine), and the long ridge running parallel to the route is full of manzanita chaparral. The Black Diamond Trail heads up to the south from here to another portion of this hike. Continue another half-mile down to the headwaters of Kirker Creek and the Nortonville townsite. I didn't see any views of the delta and points beyond because it was very hazy today, but they'd normally be in view beyond the annoying power lines.
There really isn't anything left of Nortonville except for flat ground. It looked like there was a fire here within the last 10 years. Everything has been on a fire road to this point. Take the single track Black Diamond Trail .18 mile to the Coal Canyon Trail as your route climbs both steeply and gently over the next mile through a dense short forest. Large manzanita and small buckeye hide the sun until pine trees appear in increasing numbers and size as Coal Canyon climbs up to Jim's Place. Jim evidently used to live in a small 12' deep by 6' wide by 4' high cave with a small hole in the top. There's an especially large Coulter pine right next to Jim's Place.
Go left at the road (closed to public vehicles) just beyond Jim's Place for .20 mile as it gradually climbs through a mixed pine and oak forest to the Cumberland Trail on your right. Take Cumberland about .15 mile up to the side trail to the Air Shaft. This hole in the mountain provided ventilation to an old coal mine, and it actually still goes about 30' deep. Return to the road and continue .38 mile to the Black Diamond Trail.
Black Diamond is an alternate route up to the road just below Jim's Place, and resumes its single track from the road very close to the top of a large ridge. I'm sure the views would normally be spectacular, but I couldn't even see nearby Clayton through the haze. Kinda gross. Take Black Diamond another mile and a half with expansive views of the north, east and west. Eventually you reach the Manhattan Canyon branching off to the right, and that's the quickest way down. Take it all the way down or the Chaparral Loop Trail for the remaining half mile to the parking area. The handout park map shows the locations of numerous old mining features including the developed Greathouse Visitor Center (closed today December 14, 2013) and the Eureka Slope which is a caged-off old tunnel that still runs very deep. It even has lights to show off the old mining operation.
Check out the Triplog.