GEO-QUIZ Do you know the name of the rock that forms the peaks of Telegraph Hill, Mount Tamalpais, Mount San Bruno, and Mount Diablo?

It's episode seven of the TRAIL THROUGH TIME, a series of geology videos featuring naturalist Ken Lavin. Sponsored by the Mount Diablo Interpretive Association in partnership with Save Mount Diablo. Videography by Macha Rose. Animations by Tanya Atwater, UC Santa Barbara. Music by Phil Heywood. Produced by Joan Hamilton.