Air tankers that had been fighting a blaze that destroyed at least 166 homes west of Boulder were brought in to help slow the spread of the latest fire, which has burned about 600 acres - about a square mile - about 35 miles to the north.
The fire near Loveland destroyed one home. Merlin Green, the division chief for Loveland Fire and Rescue, said firefighters were fortunate that the tankers and other resources used to fight the first fire - among the worst in Colorado's history - were available.
"It certainly could have been a lot worse," said Green, who hoped those tankers would once again be able to drop fire retardant on the blaze Monday.
The fire also destroyed four outbuildings and an RV, but no injuries have been reported. The blaze was 10 percent contained by Monday morning, officials said. A grayish haze hung over the city, partially obscuring the view of the foothills.
The blaze broke out just as residents who lost homes in the fire near Boulder were able to return to their scorched homes.
Firefighters hoped to have that fire fully contained by the end of the day Monday, a week after it started.
Like other Boulder residents, Nancy and Jim Edwards picked up a permit Sunday morning to re-enter their neighborhood, but they found out that the roads leading to their area were still closed. Jim Edwards said they might drive as far as they're allowed.
"We might take a ride, but it is really heartbreaking to see the stuff," he said.
Edwards said he spotted their house through a telescope from Flagstaff Mountain outside Boulder and saw that it was destroyed. "It looked like a nuclear disaster," Nancy Edwards said. She said they plan to rebuild.
At one destroyed property, all that remained was a stone chimney surrounded by walls of brick about waist high. Saplings in the front yard were burnt and barely their trunks remained. A barbecue grill lay upside down, along with seven metal mailboxes nearby. The house's separate garage had been reduced to a heap of ashes.
Fire officials warned that much of the area is dangerous because of downed power lines and poles, damaged roads and exposed mine shafts.
A senior law enforcement official familiar with the investigation told the Denver Post that authorities are looking into whether a resident's fire pit sparked the wildfire. The newspaper did not name the official.
The sheriff's office was aware of the Post article but wouldn't comment on the cause or origin of the fire because it's under investigation, said Sarah Huntley, a spokeswoman for the fire response. Meanwhile, authorities issued a ban on open fires effective Monday evening, barring the use of charcoal grills and campfires as well as trash and debris burns.
Hundreds of Boulder area residents evacuated since Sept. 6 returned to the dreary sight of burnt trees, melted mailboxes and uneven patches of blackened ground.
"We found grandma's sterling, melted together" said Frances Smith, who along with her husband, Mike, sifted through the ashes of their home for their belongings. They also wondered about their daughter, who was among those ordered to evacuate because of the Loveland fire.
Fire spokesman Terry Krasko said crews have been overwhelmed by the community's gratitude and are especially touched by a wall of thank-you notes at their command camp.
"That's probably one of the hardest walls for all the firefighters to go up to," Krasko said. "They really have a tough time with that. The community support has been tremendous for them."
So far, the fire has cost more than $6.7 million to contain. 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.
In Loveland, about 100 firefighters from 16 agencies were working the blaze, along with four helicopters and nine air tankers. Residents within a four-mile radius of the fire are under a mandatory evacuation order. The cause of the fire hasn't been determined.
Andy Hiller, a Loveland spokesman, said the city sent evacuation notifications to more than 1,700 phone numbers.
Six people spent the night a shelter set up in a church in Loveland. Fifty others have registered to seek help.
"I don't know if it's gone or not but it's sure hard to tell because I can't get up there," Amanda Mitchell, 31, said Sunday as she watched the air attack on the fire. She said she fears her home has been destroyed because she saw aerial footage of flames about 50 feet from the home she built with her father 10 years ago.
Peipert reported from Loveland. Associated Press Writer Ivan Moreno in Denver contributed to this report.