The town of Piedmont, and a ring of Oakland territory around it, sits on a block of bedrock of the Franciscan complex. It’s deep-sea floor material some 150 million years old that was carried across a wide ancient ocean and piled up against the edge of North America just as is happening elsewhere on Earth today. Since that time it has been sliced, shuffled, smeared and squeezed by tectonic forces, and the hill of Piedmont is one lump of a string of bedrock lumps called the Novato Quarry Terrane. This lovely piece of chert is exposed along Clarewood Drive, on the back side of Mountain View Cemetery. It displays its original deep-sea layers, somewhat jumbled and veined with silica during its later travels. More chert crops out on Clarewood Lane, which runs parallel to the Drive across a small creek.
The Novato Quarry Terrane also includes Albany Hill, Point Richmond and more pieces in Marin County. Here’s a stereopair looking from Clarewood toward Albany Hill. Click it for a big version.
Oakland Geology 
5 May 2012 at 2:35 pm
Yes, this kind of ribbon chert is very common in the Alcatraz terrane, in the places you mention.
4 May 2012 at 1:34 pm
This photo looks very similar to stones over by Coit Tower in San Francisco. I’ve also seen similar stones along the Land’s End shoreline.