The blaze was 63 percent contained late Thursday after burning 160,570 acres, or nearly 250 square miles, of wilderness northwest of Los Angeles for nearly a month.
Favorable winds helped firefighters battling the so-called Day Fire make considerable gains Thursday. Officials estimated the blaze would be contained by Monday.
Evacuations that had been urged for several mountain communities have been downgraded to precautionary, said U.S. Forest Service spokeswoman Bee Dechert.
Dozens of fire engines continued to guard mountain communities in Los Padres National Forest. But the main focus Thursday was on digging or reinforcing firelines directly on the fire's northwestern edge.
Winds were light but erratic and lookouts were posted to warn crews in case the fire suddenly changed direction.
The fire was moving slowly, feeding on dense stands of pine and thickets of chaparral, sumac and manzanita.
The National Weather Service predicted low humidity through Friday. That could dry out brush and make it easier for the Day Fire — the fifth-largest wildfire in recorded state history — to make an explosive advance.
"We're still in the red-flag warning because of the humidity," warned Randy Alvarez of the Oregon Department of Forestry, who was helping fight the fire. "But right now we have a lot of teams on it and we're in good shape. We're in better shape than we've been in days."
More than 4,500 firefighters, aided by aircraft, were fighting the blaze.
The fire has destroyed two barns, two outbuildings, three trailers, an unoccupied cabin and five vehicles.
Firefighting costs have topped $53 million. The Federal Emergency Management Agency has authorized the use of federal funds to cover some expenses.