A wildfire in mountains east of Los Angeles that has forced thousands of people from their homes was sparked by a malfunctioning diesel vehicle, fire officials have said.
The vehicle spewed burning carbon from its exhaust system, igniting several fires on Friday on Oak Glen Road in Cherry Valley.
Authorities asked anyone who may have seen such a vehicle at the time to contact investigators, according to a statement from the California Department of Forestry and Fire Protection.
The blaze in Riverside County, among several wildfires across California, had consumed more than 41 square miles of dry brush and timber since it broke out on Friday evening.
As of Monday afternoon, it was just 5 per cent contained and the fire along with coronavirus precautions made for added stress at an evacuation centre, volunteers said.
The blaze began as two adjacent fires in a rural area near the city of Beaumont, about 85 miles east of central Los Angeles.
Flames raced along brushy ridge tops and came close to houses while firefighters attacked from the ground and air.
One home and two outbuildings were destroyed, California fire officials said.
No injuries were reported.
In northern California, evacuations were ordered after a wildfire that sparked on Sunday afternoon spread quickly and burned near homes near the East Park Reservoir in Colusa County.
Complicating firefighters' efforts were temperatures in the area north of Sacramento were expected to hit 36C by Monday afternoon.
On California's central coast, a fire in San Luis Obispo County was 60 per cent contained on Monday after burning more than two square miles of brush east of the community of Santa Margarita.
Two structures were destroyed but officials said it was unclear whether they were homes.