Nearly 3,000 people have been evacuated from settlements in the parched mountains north of Los Angeles as a rapidly growing fire destroyed at least six homes, damaged 15 others and threatened hundreds more.
The blaze had burned about 40sq m (103sq km) of very dry brush in the Angeles National Forest mountains and canyons, some of which has not burned since 1929. The fire was growing so fast, and the smoke was so thick, that it was difficult to gauge its size, the US Forest Service incident commander Norm Walker said.
"This is extremely old, dry fuel," Walker said at a news conference.
The fire, which was 20% contained, appeared to be the fiercest of several burning in the west, including two in New Mexico, where thick smoke covered several communities and set a blanket of haze over Santa Fe on Saturday.
Crews fighting the two uncontained fires on Sunday were focusing on building protection lines around them amid anticipation that forecast storms could help reduce the intensity of the fires.
Crews in southern California were fighting the fire on four fronts, with the flames spreading quickest north into unoccupied land, authorities said. But populated areas about 50 miles (80km) north of central Los Angeles remained in danger, with more than 2,800 people and 700 homes under evacuation orders in Lake Hughes and Lake Elizabeth, authorities said.