The fire, which erupted Tuesday afternoon, had charred more than 10,000 acres by Wednesday morning, firefighters said.
The blaze had destroyed a mobile home, an abandoned house and a bridge, said county fire Inspector Mike McCormick. No injuries were reported.
It was only about 25 percent contained and some 2,000 firefighters were battling it.
``It's a real concern today,'' said Angeles National Forest spokesman Stanton Florea. ``If the fire continues to burn uphill into Angeles National Forest, it's going to reach some areas of real tree mortality.''
The area is thick with thousands of dead juniper and pine trees that were ravaged by six years of drought and an infestation of bark beetles.
Winds gusting up to 25 mph and temperatures in the high 90s pushed flames past ranch homes in Acton, about 50 miles north of downtown Los Angeles.
During the night, the blaze crept toward houses in the Little Rock, Bell Springs and Juniper Hills areas.
``See all the smoke? My home is right up there,'' said Cristal Herron, 42, who fled her home Tuesday with her 13-year-old daughter.
Three Angeles National Forest roads were closed indefinitely, including a popular commuter route from the growing Antelope Valley to Los Angeles.
The hot, dry weather has helped spread a series of southern California fires in the past week. Threatened communities have so far avoided the large-scale loss of homes that occurred during wildfires last fall, but officials warned that the fire season is young.
``A lot of us are looking at each other and saying 'Wait a minute, it's mid-July and this is happening,''' said Angeles National Forest spokesman Stanton Florea. ``The multiple large fires with this behavior, we usually only see after Aug. 1, and mostly in October when the Santa Ana winds are blowing.''
Elsewhere, a 6,000-acre fire near Santa Clarita was 81 percent contained and a 17,418-acre fire near Lake Hughes was 95 percent contained after it destroyed three homes and a dozen outbuildings. All evacuees had been allowed to return home.
Firefighters contained a blaze in Riverside County and made progress against a 1,600-acre fire in the San Joaquin River National Wildlife Refuge in central California's Stanislaus County.
In Yosemite National Park, a 4,200-acre fire caused by lightning was being allowed to grow on one front.
Crews in Alaska were battling a 484,000-acre fire on the outskirts of Fairbanks. Heavy smoke hampered efforts to use airplanes to douse the flames and conditions were not expected to improve this week. The blaze was considered 20 percent contained.
Wildfires already have burned 3.6 million acres in Alaska, which has been having one of its worst seasons in years.