The fast-moving wildfire in northern Los Angeles County roared through desert brush toward potentially explosive stands of dead trees Wednesday but avoided homes.
Sparked Tuesday afternoon near Acton, the Crown fire had crossed more than 10,000 acres, destroying a mobile home, an abandoned house and a bridge. With the blaze only 40% under control, city and county officials issued health and power warnings.
The latest of three large wildfires to strike Southern California this summer, the Crown fire has launched small particles and gases into the sky and reduced air quality.
Residents in neighborhoods with visible smoke should stay indoors, said Dr. Jonathan Fielding, Los Angeles County's health officer.
But some areas without smoke "still have poor air quality," he said.
"People with heart or lung disease, older adults and young children in Santa Clarita Valley, Antelope Valley and the San Gabriel Mountains should avoid prolonged or heavy exertion entirely," he said.
Los Angeles Mayor James K. Hahn urged residents to conserve electricity to reduce demand on the Department of Water and Power's transmission lines, some of which were threatened by brush fires.
"We don't have an emergency yet," the mayor said. "But we think it's important to take precautions now."
The Acton fire forced residents of hundreds of homes to evacuate Tuesday. By Wednesday, residents of all but about 30 homes were allowed to return.
Meanwhile, the Foothill fire near Santa Clarita was 95% contained after burning 6,000 acres since Saturday.
The Pine fire, which has covered 17,418 acres and destroyed three homes near Lake Hughes since July 12, was also 95% contained.
Times staff writer Zeke Minaya and Associated Press contributed to this report.