Authorities are investigating whether a fire pit sparked the devastating 10-square-mile wildfire near Boulder. The Denver Post reported Sunday that criminal charges are possible if investigators determine that the wildfire was started by an untended fire pit. The newspaper attributes the information to a senior law enforcement official familiar with the investigation. The newspaper did not name the official. Boulder Sheriff Joe Pelle previously said investigators initially believed the fire was started by a vehicle that crashed into a propane tank.Meantime, fire teams battling the Fourmile Canyon Wildfire are growing increasingly confident that they've been able to stop it from spreading so that some 1,000 evacuees can soon return to their homes -- or what remains of them. Boulder authorities said Sunday that residents from another subdivision ravaged by the wildfire will be allowed to return to their homes for good, but they warned that much of the area is dangerous because of downed power lines and poles, damaged roads and exposed mine shafts. Still, utility workers were restoring electricity to homes where about 2,000 residents have been allowed to return in the rugged foothills above Boulder. Firefighter Steve Reece spent Saturday day digging out grass and cutting through roots with a tool that's part shovel, part hoe and part ax to snuff out hot spots. "We had a good day," Reece said. The Fourmile Canyon fire erupted Sept. 6 and quickly destroyed at least 169 homes. It was 73 percent contained Saturday night and crews, taking advantage of calmer winds, hoped for full containment by Monday evening. Some 1,000 firefighters from 20 states dug lines and tamped out hot spots. "It's great. We're looking better and better," said Jim Thomas, head of the federal incident response team leading the effort. Fire spokesman Terry Krasko said Sunday operations are beginning to be scaled back and some crews are being relieved. An infrared flight over the burn area showed several areas of isolated heat but no large pockets of intense heat, as previously seen. Firefighters focused on those areas, especially ones near buildings. The Boulder County Sheriff's Office planned to issue passes Sunday to residents from the hardest hit areas so they eventually can access their property without impeding firefighters or police. But Cmdr. Rick Brough said it wasn't known when or which roads, some heavily damaged, will be reopened to those areas. Inside the burn area Saturday, crews worked to snuff out smoldering stumps, using shovels, axes and water carried on backpacks. Fire trucks and water tenders ferried water up the mountains and down the canyons while helicopters dropped water on hot spots. "There is a lot of unburned fuel and a lot of houses at risk," warned Don Ferguson, a spokesman for the incident command. The fire left some houses standing among blackened forests while homes nearby burned to the ground. Burnt cars littered driveways. At one home, a winding stucco concrete staircase rose about 15 feet into open space -- where a house used to be. Beyond, mountains in the distance sprouted 100-acre patches of burned trees surrounded by green forest and untouched homes. In the town of Gold Hill, Mayor Amy Hardy and other volunteer firefighters prepared for residents' return. "We're getting frozen food out of freezers before it spoils, feeding livestock, chickens," Hardy said at the Gold Hill Inn. Xcel Energy, the region's electricity utility, planned to start repairing or installing new poles and lines, said spokeswoman Michelle Aguayo. It has cost more than $6.7 million to fight the fire, which was quickly fanned by gusting winds. Winds picked up again later in the week, leading to fears that the fire might spread into the city of Boulder. Officials urged residents to prepare to evacuate, but fire lines held and no evacuations were needed. Authorities believe the blaze was human-caused. They are looking at whether a vehicle may have crashed into a propane tank. The loss of homes surpassed that of the 2002 Hayman fire in southern Colorado, which destroyed 133 homes and 466 outbuildings over 138,000 acres, or more than 215 square miles. Insurers had no immediate damage estimate for neighborhoods filled with a mix of million-dollar homes and more modest log homes and ranches. Carole Walker, executive director of the Rocky Mountain Insurance Information Association, said the blaze affected mostly primary residences, not vacation cabins, so lost homes are more likely to be insured. The Boulder Daily Camera reported the wildfire destroyed at least $76.9 million worth of property, based on a database of buildings confirmed burned and their valuations listed in Boulder County property records.