Crews continued cutting vegetation Wednesday in the Mount Graham communities of Columbine and Turkey Flat, where cabins had been drenched with water and wrapped with aluminum to deflect heat.
Two fires were burning on the southern and western sides of the mountain.
Officials were hopeful that they could save the Mount Graham International Observatory, which was surrounded by a broad cleared area and had sprinklers.
The same blaze nearing the observatory was about 1 1/2 to 2 miles from Columbine, a community of some 15 homes and cabins.
The second blaze was between the observatory and Turkey Flat. It was within a mile of Turkey Flat on Wednesday and officials were worried that it would strike the community of about 74 summer homes, said fire crew spokesman Bill Duemling.
The two fires had earlier prompted evacuation of the observatory and both communities.
``There's a good chance we will lose structures,'' said Dan Oltrogge, an incident commander for the team fighting the fire. ``But we're doing everything we can to keep the fire out of there.''
Officials said the blazes had charred more than 22,100 acres combined. Both were 10 percent contained.
Flames swept across a peak holding two communications towers and a historic cabin on Tuesday. Some structures were damaged and some agencies' communications functions were compromised, fire officials said Wednesday, but they had no other details on damage.
Scientists feared that the fires could devastate the only population of Mount Graham red squirrels, an endangered species already imperiled by insect outbreaks attacking the forests, habitat loss and long-term drought.
At Turkey Flat, fire crews wrapped sheets of aluminum around cabins to deflect heat and drenched them with water.
Gherald Hoopes, who owns a home in Turkey Flat, said he was ``kind of resolved'' that the fire would reach the community.
``It just has one canyon and then it will run right up to the cabin,'' Hoopes said. ``It would be a significant loss... We really wouldn't be able to replace it.''
The observatory's protection, including a sprinkler system, had been reinforced by strengthened protection lines and prescribed burns.
Home to some of the world's most powerful telescopes, the observatory encompasses eight buildings and 8 1/2 acres of pine forest on Mount Graham's 10,470-foot Emerald Peak. Although its metal structures should withstand the flames, officials said smoke and heat could damage delicate instruments.
The observatory has two operating telescopes and the $120 million Large Binocular Telescope, which is under construction. When fully operational next year, the Large Binocular Telescope will be the world's most advanced optical telescope, capable of producing images nearly 10 times sharper than those from the Hubble Space Telescope.
Elsewhere in Arizona, a fire had blackened 90,500 acres of the Tonto National Forest near Payson, a town of some 14,000 people. The blaze was 22 percent contained on Wednesday and was not threatening any homes or communities.
In Alaska, hundreds of residents evacuated last week because of a huge wildfire northeast of Fairbanks were allowed to return home Wednesday. Thanks to lower temperatures, intermittent rain and higher humidity the fire had been 27 percent contained. It had charred 312,000 acres of the more than 2 million acres burned statewide.
In central Washington state, two wildfires had blackened more than 11,000 acres near Lake Chelan. One fire, only about 3 miles east of Lake Chelan in north-central Washington, had covered 4,205 acres but was about 50 percent contained, fire spokesman Nick Mickel said Wednesday. Officials had recommended evacuation for residents of about 45 homes.
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