The Mountain fire in Riverside County, first reported Monday, had burned about 8,000 acres late Tuesday, the Los Angeles Times reported.
Lee Breyer, a spokesman for the U.S. Forest Service, said much of the fire is in areas that cannot be reached by road. More than 2,000 firefighters are on the scene, helped by 25 aircraft.
Hot, gusty winds are complicating the effort to get the fire under control. Breyer said it is burning through areas of old chaparral.
Officials said it had gutted three houses, three mobile homes, several outbuildings, a garage and a commercial building as well as four to six vehicles.
Residential areas, the Living Free animal sanctuary and the Zen Mountain Center were all ordered emptied.
While the fire was 10 percent contained Tuesday, officials said high winds were shifting the flames east. It affected communities including Pine Springs and Mountain Center.
"It's super steep, and a lot of brush and trees," Carol Jandrall, a spokeswoman for the Forest Service, said Tuesday. "It's very difficult to fight, and it's hot."