The Claremont chert actually has the official name Claremont Shale, and I should stop calling it Chert-with-a-capital-C. The rock unit was first named by Andrew Lawson, UC Berkeley’s memorable professor of geology who masterfully conducted and wrote up the scientific studies of the 1906 earthquake. (Lawson has the mineral lawsonite named for him, too. I hope to find some in Oakland some day.) Lawson named the Claremont Shale because the unit is predominantly shale, even though in Claremont Canyon, as in the rest of Oakland, it’s quite cherty.
When geologists name a rock unit for the first time, they designate a type locality and take the name from that. They also designate a type section, a specific place where anyone can visit and check the definitive example of the XYZ Formation. They draw a detailed stratigraphic column from the type sectionit’s sort of like an engineering drawing, very formal. And they publish a detailed description of the unit and the stratigraphic column in a reputable journal or government-issued publication. The type section is supposed to display the top and the bottom of the formation and, ideally, everything between. The US Geological Survey has a panel of experts who do nothing but keep track of geologic names, both for rock formations and for the Eocene/Jurassic/etc. geologic time units. I used to work across the corridor from one of them, and he was quite the specialist.
So Claremont Canyon is the type locality for the Claremont Shale. Lawson’s original description is in US Geological Survey Geological Atlas Folio 193, published in 1914. The UC Geology Library probably has a copy. And this exposure of the chert along upper Claremont Avenue must make up part of Lawson’s stratigraphic column in that old atlas.