The Rockridge Shopping Center quarry is in pretty good shape . . . for a Bay area quarry. Most of the rocks in the Coast Ranges are battered and shattered to various degrees, what with being ripped apart and shaken and squeezed into hills by the activity along the San Andreas fault system. Most of this former quarry is holding up well. But the whole length of the rock face has a chainlink fence in front, with piles of rubble trapped behind it. This spot is near a zone of dark, serpentinite-looking rock that has been failing more than the sandstone and lava around it. If these stout timbers can’t deal with it, I doubt the fence will help much when the rest of the slope starts to give.
Rock naturally deteriorates when you strip the soil off it. Actually the soil is made of deteriorated rock itself. Solid rock may be overrated.
Oakland Geology 