Fire managers began releasing engines and air power from a fire Saturday that destroyed at least 15 homes as crews secured containment lines near homes and made progress in the Sierra backcountry to keep the flames out of the Lake Tahoe (search) basin.

Meanwhile, officials broadened their investigation of the fire's cause. They initially said they suspected the blaze was started by teenagers in Kings Canyon (search) the day before the fire erupted Wednesday, but said Saturday the fire could have started last weekend and smoldered undetected for days.

The wind-driven blaze, which scorched nearly 7,600 acres, also destroyed a business and 25 outbuildings. It was 85 percent contained Saturday, and no longer posed an imminent threat to communities in northwest Carson City (search) or surrounding areas in Washoe Valley, officials said.

Fire officials said the blaze could be fully contained by Tuesday with good weather.

"They're getting a very good handle on it," fire information officer Mark Struble said at a press briefing. "If we can hold these lines for another 24 hours, it'll be very, very good."

Hundreds of evacuees were allowed back home late Friday, but some of them on Saturday questioned whether firefighters could have done more to stop the blaze in its early stages.

"This atrocity should never have happened," Washoe Valley resident Betty Kelly said at a town hall meeting Saturday. "There was too much waiting and seeing."

Bill Bettridge, whose home in the Kings Canyon area was spared, suggested fire managers provide the community with a timeline on what action was taken when the pre-dawn fire was reported Wednesday.

Fire officials defended their response, as did some residents.

"They moved so fast to try to control it," said "Mike" Gutter, who watched the fire unfold from her home near Kings Canyon. But the afternoon wind "flattened it out like a pancake and spread it in all directions," she said.

Gusty winds out of the west pushed the wildfire in different directions. Fueled by trees and brush brittle by five years of drought, the fire swept through the area unlike any seen in Carson City's history, officials said.

Nearly 2,000 firefighters remained on the lines Saturday, assisted by more than 120 engines and water tenders, bulldozers and aircraft that included three heavy air tankers.

Meanwhile, in California, hundreds of people were forced to evacuate Saturday when a wildfire broke out in northern Los Angeles County. The 2,800-acre blaze threatened Sand Canyon, a community of more than 100 homes, Placerita Canyon and the Placerita Nature Center.

About 750 firefighters were on the scene, battling the blaze with water-dropping helicopters. No homes or structures had been destroyed, officials said. Fire officials said the fire was 30 percent contained by late Saturday.

Another wildfire in the area shifted away from two rural communities, allowing hundreds of residents to return to their homes. The fire in Lake Hughes had blackened 16,800 acres, but was about 70 percent contained, officials said.

A wildfire in Riverside County, about 90 miles east of Los Angeles, threatened nearly 700 homes and forced the evacuation of about 2,000 people, officials said.

Fire department spokeswoman Madeline Lopez said the fire, which had grown to 3,219 acres by late Saturday, apparently broke out earlier in the day when someone shot a gun in the brush. The person was cited would likely a pay portion of the costs to put out the fire, Lopez said.

The blazes were among dozens of wildfires in California that burned more than 31,000 acres during the week. Karen Terrill of the California Department of Forestry said her department found 200 fires in 48 hours.

In Washington, crews held down a blaze that had damaged 700 acres by Saturday west of Leavenworth, a Bavarian-theme tourist town. Another fire northeast of the town was nearly 70 percent contained. No major injuries or property was reported in any of the fires.