Hematite, the mineral form of iron oxide, was highly prized by the Ohlone and Miwok triblets surrounding San Francisco Bay. It was the principal source of red ochre, used in burials, ceremonies, and pigments. Hematite outcroppings near the intersection of Redwood Road and Mountain Boulevard in Oakland undoubtedly supplied much of the prehistoric Bay Area. The worked hematite deposit nearest this one was in Petaluma about 50 miles away.
Skilled prehistoric quarrymen hammered out or pecked away chunks of hematite from this boulder.