The other week I took a hike up Claremont Canyon, one of those parts of Oakland that everyone thinks is in Berkeley. Walking there is slightly dicey because the road is narrow and cars don’t expect pedestrians, but I plan to do it again. The bedrock shifts from nondescript sandstones of the Great Valley Formation to vertical stripes of Claremont Chert, to coarse conglomerate of the Orinda Formation, then basalt of the Moraga Formation near the top. That’s what this is. According to the map, this must be float—loose stones carried downhill in the soil—rather than actual bedrock. The fresh rock is black and the weathered rock is brown. This is the stuff exposed throughout Sibley Volcanic Regional Preserve, but you can’t collect it there. You probably can’t collect this either, because Claremont Canyon is also a reserve, but nobody cares about roadcuts. Still, I try to observe these things because I talk to the public and really need to set the right example. You can collect it in the fantastic exposures along Route 24.
As you continue south on Grizzly Peak Boulevard from the top of Claremont Canyon road, you can look back and follow the basalt along the hillside, over the crest, across Route 24 and up toward Round Top. This is a hard region to map, but the Moraga basalt is easy.
Oakland Geology 
24 February 2008 at 3:32 pm
Basalts can be fun, in my study area in south east Missouri, the St Francis region, there are a couple outcrops that are fascinating, one is where basalt dike intrudes a rhyolite mass, and both are exposed in a road cut (if you want the location, ill have to look it up). At that location you can see the differential weathering of the high energy state basalt, and the lower state and more resistant rhyolite. There is also a really cool basalt dike exposed in a river valley at Silver Mines Campground that has received quite a bit of study from students at my alma mater, one of the few locations in the world of a quartz basalt, that’s right, a quartz basalt. See, basalt can be fun.