The big fire started around 3 p.m. Friday in remote Alameda County, just south of Sunol. Crews reported full containment around 9 a.m. Saturday.
More than 200 firefighters battled the flames, steep terrain and heat as the fire quickly ate up the dry brush and grasses on the hillside.
The point of origin is believed to be right next to Calaveras Road. Fire investigators will be looking for incendiary accelerants that might have caused this fire, if it had been set.
The land is owned by the San Francisco Water Department. It is part of the Hetch Hetchy water system.