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Sue Ogrocki, Associated Press
A helicopter drops a load of water onto a grass fire in Medicine Park, Okla., Friday, June 24, 2011. Twelve home have been destroyed by the fire that has blackened more than 5,000 acres.

MEDICINE PARK, Okla. — Churning fire described as a "wall of flame" threatened a remote Oklahoma resort town Friday, pushing through dry brush on 30 mph wind gusts after destroying at least 13 homes.

Comanche County authorities ordered more than 1,500 people from their homes along the northern fringe of the Fort Sill U.S. Army post. Fire crews attacking the blaze on the ground and from the air had the 5,500-acre fire about 40 percent contained by Friday afternoon.

High winds refueled the blaze, pushing it farther northeast across Oklahoma Highway 58 south of Lake Lawtonka, county spokesman Chris Killmer said. Additional homes were evacuated before crews contained the flare-up about an hour later, Killmer said.

The fire spread a thick, smoky haze over the foothills near the Wichita Mountains Wildlife Refuge.

"The humidity is really low, there's high winds and it's very rough terrain," said Medicine Park Fire Chief David McCoy. Weather forecasters imposed a red flag warning Friday for temperatures of up to 108 degrees, winds of 20-30 mph and humidity readings below 20 percent.

"I've never seen it in my life as dry as this," said Doug Wright, chief of the Paradise Valley Volunteer Fire Department, which sent 18 firefighters to help battle the blaze. "We never fight major fires in June and July because it's usually green."

The fire began Thursday afternoon on the military post and spread northward toward this old resort town between the Wichita Mountains and Lake Lawtonka. Small fires also dotted the nearby mountains 80 miles southwest of Oklahoma City.

In addition to the six houses and seven mobile homes burned, fire had also consumed several sheds, barns, detached garages and storage units, Killmer said. At Fort Sill, officials asked post personnel to not water lawns or wash their vehicles until the fire is out.

One firefighter suffered a minor foot injury but no other injuries have been reported, Killmer said. Firefighters from more than 25 departments responded to the fire and about 60 firefighters battled it Friday morning. An Oklahoma National Guard helicopter team from Lexington began dropping water on the fire shortly before noon, and another helicopter was dispatched to help, Killmer said.

Officials at Fort Sill believe the cause of the fire to be "military training," spokeswoman Emily Kelley said, "but the investigation has not yet started because our firefighters' entire mission at this point is fighting and containing the fire. Once that is accomplished, there will be an investigation into the specific cause."

Fort Sill Fire Chief Clint Langford said artillery practice takes place daily at the post's West Range, where the fire started. He said there are several fire breaks along the range to prevent fires, but high winds and woody debris left over from recent ice storms quickly fueled the blaze.

The rocky, rough environment made it difficult for firefighters to get their vehicles and equipment into place to fight the wind-whipped fire.

"It's impossible," Wright said. "It's really a defensive fight because of the terrain." He said the strategy has been to set up defensive positions around homes and other structures and "wait for the fire to come to us."

The state Highway Patrol closed portions of Oklahoma 49 and Oklahoma 58, which lead into town.

Jim Ware, who lives north of Medicine Park, said he was outside his home Thursday night when a Comanche County sheriff's deputy drove by and told him and neighbors to leave because the fire was half a mile away.

"It was a massive wall of flame," said Ware, 71. "I'd be surprised if they got it under control before it got to the houses on my road."

Ware said he grabbed some important papers, a few clothes and his computer "and I got out of there." He spent the night at a relative's home in nearby Lawton and still didn't know Friday what had happened to his home.

Another resident, Jackie McKown, said that as she was evacuating Medicine Park on Thursday night, she looked back and "the mountain behind our home was totally in flames."

Authorities set up a shelter at a gym on Fort Sill and in an American Legion building in Medicine Park. American Red Cross spokesman Rusty Surette said the Red Cross is assisting at those shelters but is not operating them.

The Medicine Park water treatment plant, which supplies the majority of water for Lawton — a city of 93,000 — remains in operation, Killmer said. Fort Sill officials said the plant is running on backup power.

Parts of western Oklahoma have been plagued by exceptional drought in recent weeks, with conditions exacerbated by dry conditions and hot weather.

Temperatures in the region are forecast to be above 100 degrees Friday with winds gusting up to 30 mph. The National Weather Service issued a red-flag fire warning for 17 western Oklahoma counties.

Associated Press writer Murray Evans in Oklahoma City contributed to this report.