With another tinderbox summer shaping up in much of the West, officials issued red-flag fire warnings for Colorado on Thursday, while in Arizona a roaring blaze forced the evacuation of about 1,000 homes.

Wildfires also were burning in Alaska and Utah.

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The aggressive 700-acre Colorado blaze had already prompted about 100 people to leave their homes in the rolling hills near Westcliffe, about 100 miles south of Denver.

The fire, which began when a falling tree dragged a power line to the ground, left patches of dense trees and brush "totally nuked, completely black," said Steve Segin, a spokesman for the Rocky Mountain Incident Management Team.

Air tankers became unnecessary Thursday afternoon when the wind direction shifted to push the fire back onto itself, Segin said. Air tankers and helicopters were available if needed.

No structures were reported lost, but a house suffered exterior damage. A six-mile stretch of Colorado 96 was closed.

Judi Coker, who lives about two miles from the fire, said less smoke was visible Thursday than a day earlier. Her subdivision was not threatened and she and her husband, Rod, were not among the residents who left, but their bags were packed just in case.

"It's very dry, more dry than I've seen it since we lived here," said Coker, who has lived in the area for four years.

The Rocky Mountain Area Predictive Services issued a red-flag warning for a huge swath of southern Colorado, meaning conditions were favorable for big, fast-moving fires. The warning spanned the entire width of the state and ranged as far north as the Denver area.

At least 60,604 acres have burned in Colorado this year, said Larry Helmerick, spokesman for the Rocky Mountain Area Coordination Center. That compares with 41,048 acres for all of 2005. It was still far below the 619,029 that burned in 2002.

"It's so dry out here that it doesn't take more than a spark to start a wildfire," said Jamie Moore, director of emergency management for Douglas County south of Denver, where a passing train apparently sparked a 30-acre fire Wednesday.

In northwestern Colorado, a 3,700-acre fire quieted down after high winds blew in a mild cold front, said fire information officer Pam Wilson. One abandoned cabin burned.

More than half of Colorado is experiencing severe or extreme drought, according to the National Drought Mitigation Center. Arizona is almost entirely under extreme drought conditions.

In Arizona, fire crews quickly responded to a 120-acre blaze that broke out Wednesday afternoon on the west side of Flagstaff, a city of 60,000 people nestled in a thick pine forest. The blaze was contained Thursday morning, but the threat was enough to evacuate 1,000 homes.

Officials credited the quick response of air tankers and extensive forest thinning.

Jim Wheeler, the assistant fire chief in Flagstaff, passed the word to a meeting of evacuees Thursday that all the area's homes were saved.

"Your neighborhoods are in fantastic shape," he said to loud applause.

In Alaska, a wildfire only a few miles northeast of the small town of Anderson grew to 65,500 acres. The town, 75 miles southwest of Fairbanks, was not in immediate danger, fire officials said Thursday.

Nearly 300 firefighters fought a 2,500-acre fire on the Utah side of Navajo Mountain on the Navajo Indian Reservation. The blaze was believed to have been started by lightning Saturday, said Jim Whittington, a U.S. Bureau of Land Management fire information officer in Kingman, Ariz.

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So far this year, nearly 2.9 million acres have burned. That is more than three times the average by this time of year, according to the National Interagency Fire Center, but much of the acreage came in huge grass fires that swept Oklahoma and Texas this spring.