More than 3,800 acres of the San Bernardino National Forest have been scorched since the fire started on Tuesday in the heavily developed area about 50 miles east of downtown Los Angeles.
Billowing clouds of smoke hung above the area as the California Highway Patrol ordered closure of Interstate 210, an east-west highway running north of Los Angeles, and Interstate 15, the main route from Southern California to Las Vegas.
Evacuations were ordered yesterday morning for hundreds of residents in north-eastern Rancho Cucamonga, and about 2,000 people were ordered out of the nearby Lytle Creek area because the blaze was expected to block the only road into the area.
About 1,400 firefighters battled the blaze, which was only 17 percent contained early yesterday.
Triple-digit temperatures were expected yesterday, and winds of 25 mph and up were reported. Even stronger winds are expected to pick up over the weekend.
The fire, which authorities have blamed on arson, was one of several that swept through southern California this week, destroying five homes and chewing through nearly 11,000 acres.
A fire near Piru in Ventura County had charred about 700 acres by early yesterday but was burning away from homes, said Barry Peckham, a spokesman for Los Padres National Forest.
At Camp Pendleton Marine Corps Base, 50 miles north of San Diego, 1,350 firefighters were battling a 4,100-acre brush fire that was threatening 300 homes yesterday morning. Residents were asked to evacuate and a temporary shelter was set up.
Officials said the fire started on a training range on Tuesday, apparently sparked by ammunition used in military exercises, and was 40 percent contained early yesterday. Firefighters have been unable to enter the south-western area of the fire because it could be littered with unexploded ammunition.
A 2,857-acre fire in the Reche Canyon area of Riverside County had been completely contained by Thursday evening. It had destroyed five homes, a barn, 21 outbuildings, a boat and several vehicles.