On the south side of Los Berros Creek the hill is made of volcanic tuff, old ash cemented into a pale stone that saws cleanly and, in its lower bed, rings when you strike it and breaks with curved glassy faces. A century ago that was worth money.
The Moore quarry, owned in Arroyo Grande and leased to a Los Angeles concern that called itself the Los Berros Stone Company, cut the tuff in two layers, the softer upper bed ten or twelve feet thick and the harder bed beneath it. A gang-saw mill down in the creek dressed the blocks. They went into buildings in Arroyo Grande and San Luis Obispo, and by rail and ship through Port Harford to Los Angeles. The state mineralogist found the quarry working in 1906. By the 1915 survey it had been idle for years and the machinery was gone.
The quarry is on private land and there is nothing to see from the road. But the stone is still in the walls of a few old buildings in the county, and the creek still runs past the cut where the saws once stood.