View photos of the edible and medicinal plant, Rubus ursinus (California blackberry), profiled in the Wild Edible Series: California.

A passage from Wild Edible Plants of California:

When ripe, Blackberry fruit (not an actual berry but a drupe) are dark purple to black, and usually smaller than store–bought. They are sweet, mildly tart, and delicious when gathered from a healthy and well–hydrated specimen.