As of midday, the flames were two miles from Turkey Flat, a community of 74 cabins on the side of Mount Graham. But officials said the 8,550-acre blaze could spread quickly in the hot, dry weather.
``We could very well lose some homes today or tomorrow,'' said Pruett Small, an operations chief for the fire management team.
The lightning-sparked fire and an nearby 7,810-acre blaze on another part of the mountain in southeastern Arizona had earlier prompted evacuation of the Mount Graham International Observatory and a total of about 90 cabins in Turkey Flat and another community.
The observatory's eight buildings and 8 1/2 acres of pine forest on Mount Graham's 10,470-foot Emerald Peak were surrounded by a 200-foot-wide clearing, and fire crews planned more controlled burns to expand the buffer zone. It also has a sprinkler system that officials said would be turned on if flames got to within a quarter-mile.
``Every day it gets a little bit better at the observatory,'' Small said.
Officials said that while the observatory building would probably not burn, smoke and heat could damage its delicate instruments.
The observatory, an extension of the University of Arizona, 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.
Fire crews' main concern Tuesday was Turkey Flat, lower on the mountain about 150 miles southeast of Phoenix. Firefighters removed heavy vegetation from around cabins and drenched the homes with water, while wrapping them with aluminum to deflect heat.
Small said officials planned to decrease the number of firefighters in Turkey Flat because of the danger of the blaze making a strong run.
``I don't want anyone's life put in jeopardy because of my cabin,'' said Richard Lines, 59, who has owned his Turkey Flat summer home for 25 years. ``Everything is replaceable, but a life is not.''
Elsewhere in Arizona, a fire had blackened 85,000 acres of the Tonto National Forest near Payson, a town of some 14,000 people. The blaze was not threatening any homes or communities.
In Alaska, an evacuation order remained in effect Tuesday for 277 homes threatened by a 307,000-acre fire north of Fairbanks.