The Apple Fire in Riverside County consumed more than 31 square miles of dry brush and timber, according to the California Department of Forestry and Fire Protection.
As of Monday morning, it was 5% contained. The cause was under investigation.
The blaze began as two adjacent fires reported on Friday evening in Cherry Valley, an unincorporated area near the city of Beaumont about 85 miles east of central Los Angeles.
Flames leapt along brushy ridge tops and came close to homes while firefighters attacked it from the ground and air.
One home and two outbuildings were destroyed, Cal Fire said. No injuries were reported.
Evacuation orders and advisories were issued for about 8,000 people in mountain, canyon and foothill neighbourhoods.
Campgrounds and hiking trails were closed in the San Gorgonio Wilderness area of the San Bernardino National Forest.
A huge smoke plume was visible for miles around and contributed to poor air quality.
The mercury hit 109F (43C) on Sunday in nearby Palm Springs.
The National Weather Service said “dangerously hot conditions” were expected to continue because of high pressure over much of southern California.
To the north, the Pond Fire in San Luis Obispo County was 10% contained on Sunday after burning more than two square miles of brush east of Santa Margarita. The blaze destroyed two structures but officials said it was unclear whether they were homes.
