Right on the border between the state park and the Mt. Diablo Foothills regional park is this awesome formation:
(credit to ParsecTraveller, whose photos are almost too good.)
I stumbled across it during the East Bay Hash's 30th anniversary, where I showed up two hours late (surprise) and running it all by my lonesome, got badly lost (surprise again). But I found this place, so it was worth it.
Pu’u Oo Trail, Big Island Hawaii
41 minutes ago