A photo of volcanic rocks.

The Point Reyes Conglomerate of Galloway (1977) contains clasts that represent an assortment of different rock types; most are of volcanic origin. The person’s finger points to a dark andesitic porphyry (tuff) that contains small, pink feldspar crystals. This striking lithology can be seen in conglomerate beds throughout coastal California extending from Ventura to Point Reyes. The conglomerate and granitic rock at Point Reyes correlate with the Carmelo Formation and Monterey Granodiorite at Point Lobos south of Monterey, California (Burnham, 1999).