Helicopters and air tankers bombarded a wind-driven 3,500-acre wildfire with water and flame-retardant Tuesday as firefighters struggled to protect some 2,100 evacuated homes.

The blaze, which began Monday in the forest east of the cities of Anaheim and Orange, was only 7 percent contained, said Dennis Shell, a spokesman for the Orange County Fire Authority. The cause of the fire was under investigation.

Dry desert winds gusting up to 40 mph hampered the 900 firefighters as they worked to beat the flames back.

Some residents managed to return to evacuated neighborhoods, and some never left.

Don Cosgrove kept watch on his home in an Orange neighborhood after refusing to evacuate Monday night. He said he was particularly worried about his wood shake roof and the older vegetation in the neighborhood, which is more than 25 years old.

"I'm concerned about embers," he said. "The firefighters are focused on other areas, and by the time they'd be able to respond it would be too late."

Crews took advantage of calm conditions during the night to light backfires to burn off fuel.

On Monday, a towering plume rose over the Santa Ana Mountains and smoke stained skies brown for miles across Southern California. Ash fell on downtown Los Angeles, 35 miles to the northwest.

"The ash was coming down like snow. I had all the windows and door shut because it was just overwhelming," said Kathie Scott, who was ordered by a firefighter to evacuate her Maybury Ranch home.

The Santa Ana winds have often played a role in disastrous wildfires. In 2003, wind-driven wildfires destroyed more than 3,600 homes and killed 22 people in Southern California.