This is Oakland’s northernmost point, a little wedge of land between Summit Road and Tilden Park. It’s mainly occupied by a large EBMUD water tank and is supposedly underlain by Moraga Formation basalt, though I didn’t see any.
Oakland’s southernmost point is a runway at the airport, a place I expect never to visit, although I’ve certainly flown over it enough times. But that’s artificial fill. The southernmost bit of real land seems to be just north of the San Leandro water treatment plant between the end of Eden Road and Davis Street.