FORT COLLINS, Colo. — Hundreds of firefighters worked Thursday to combat a growing blaze that was scorching terrain around a scenic canyon in northern Colorado.
Ground efforts were being supported by a heavy air tanker and helicopters that together are capable of dropping thousands of gallons of fire retardant and water on the spreading flames.
U.S. Forest Service officials said the blaze about 20 miles northwest of Fort Collins grew from about 1.5 square miles to more than 11 square miles Thursday amid erratic winds gusts of up to 50 mph. The fire was approaching the city of Greeley's Milton Seaman Reservoir on Thursday night, but city officials said Greeley's water supply hasn't been affected.
Authorities ordered mandatory evacuations of about 80 homes near Poudre Canyon earlier in the day, even going door to door to issue warnings.
Residents of about 65 of those homes were allowed to return by early evening, with instructions to be ready to leave again if conditions change.
Officials think human activity started the blaze, which was first reported Monday, but they are still investigating.
The Colorado fire was one of several burning in the West on Thursday.
A fire in northern Arizona that led to the evacuation of a historic mining town grew to more than 10 square miles even as the outlook improved from earlier in the week.
Forest Service spokeswoman Michelle Fidler said that wind pushed the fire north, and crews focused on slowing the blaze from the west, where communication towers are threatened.
Most of the 350 residents of the mountain community of Crown King, about 85 miles north of Phoenix, had already cleared out Thursday.
The fire prompted an evacuation order Sunday and has destroyed three homes and a trailer. The blaze started at a home, but investigators were still working to determine the cause.
Other fires dotted Arizona but did not threaten any structures, authorities said.
Meanwhile, separate blazes in northern and southern New Mexico cast a haze of smoke over the state but have not caused property damage or prompted evacuations, authorities said.
A wind-fueled fire in western Utah closed a state highway but wasn't threatening any structures.
The Colorado fire is scorching a drought-stricken area of steep, rocky terrain scattered with dry ponderosa pine trees, grass and shrubs. The region north of the Cache La Poudre River is popular with hikers and rock climbers.
About 400 firefighters worked to get control of the blaze, and more air tankers and a large helicopter were requested earlier Thursday.
A thick smoky cloud over Fort Collins prompted health officials to warn that children and people with lung or heart problems should stay indoors.
The haze extended 65 miles south to Denver, leading to concerns that it would affect flights at Denver International Airport, but officials there said operations had not been delayed.
A human-caused fire near Fort Collins in April 2011 scorched 5 square miles, destroyed 13 houses and temporarily displaced residents from 335 homes.
Though the evacuations Thursday were mandatory, officials are not authorized to forcibly remove anyone from their homes.
Area resident John Hasler said he wouldn't leave.
"We're not going to have a fire come down and burn our house," Hasler said, adding that his home is surrounded by a lawn of closely cropped grass. "If it does, it'll burn grass and it wouldn't be big flames. I'm really confident that I can handle it with my garden hose."
Hasler said "it's a totally different situation" from the late March wildfire that killed three people south of Denver.
This blaze is the first wildfire to warrant evacuations in the state since those deaths.
"If my home was in the timber," Hasler said. "I'd be really worried."