CASTLEFORD - One of the largest fires in Idaho history continues to burn out of control southwest of Twin Falls, officials with the U.S. Forest Service said Monday.

This fire and others burning throughout Idaho prompted Gov. C.L. "Butch" Otter to declare several southern Idaho counties disaster emergency areas.

Firefighters are calling the Murphy Complex fire, which has torched nearly 600,000 acres, the largest Idaho wildfire since a 1910 blaze that burned three million acres. The Murphy fire threatens 7,500 residences, 1,000 commercial properties and 500 businesses from Castleford to Mountain City, Nev., and the scope of the blaze and the terrain it covers has firefighters wringing their hands.

"This is probably the biggest fire we've seen in the U.S. since 1910," said San Diego-based Rich Hawkins of the Forest Service, who is coordinating the firefighting efforts from a command post in Castleford. "This fire has the potential to become one of the worst fires in American history."

That's if the fire continues to burn north through grassland toward the Snake River Canyon. But as of Monday, the fire looked to be headed south farther into Nevada's mountainous terrain. The tiny town of Jarbidge, Nev., was evacuated last week, and the fire continues to burn in its direction.

The Murphy Complex is close to linking with the Three Creek Fire near Jackpot, Nev., and it's likely the Murphy firefighting team will take over management of that blaze today.

Officials may call in a second top-level management team later this week if the fire continues to grow, said Pam Bierce, a fire information officer with the Forest Service.

The Murphy fire also threatens training ranges at the Mountain Home Air Force Base, where pilots train before missions to Afghanistan and Iraq. But the blaze is yet to damage property there.

"There is no part of the fire on our training range and there is no impact to Air Force resources at this moment," said Lt. Erin Tindell, a spokeswoman for the base.

Ranchers are bearing the brunt of the damage. Rep. Bert Brackett, R-Rogerson, has lost at least 50 cattle that were burned to death over the weekend. His family is scrambling to load livestock into trucks on grazing land in Nevada.

"I've seen big fires before," he said. "But this is like 30 years of fires just this year."

Firefighters are updating ranchers of fire conditions in the field, Bierce said. "There's just so much grazing land that has been destroyed. This is really affecting ranchers."

Also affected: precious Idaho wildlife. Bull trout, big horn sheep and sage grouse are in danger. Brackett said his son told him he saw jackrabbits burnt alive spread the fire across rural roads.

Firefighters are relyinglargely on aerial crews to battle the blaze. The heart of the fire is burning nearly four hours away from the fire's command post in Castleford, making it difficult for crews to rotate in and out. Some crews have been in the field for three consecutive days.

Aerial crews deployed from Twin Falls' airport flew continuous missions over the blaze Monday, dropping fire retardant on the fire's perimeters. Late last week, the Bureau of Land Management's air-tanker base at the airport loaded more fire retardant onto planes than it ever had before, said Carlos Mendiola, the air-tanker base manager. He said the base will set a record for retardant used in a single season by summer's end.

Mendiola expected to stay busy throughout the week. Lightning storms are predicted to strike near the fire, and fire manager Hawkins and others expect thousands more acres to burn before the fire is contained, perhaps sometime around Aug. 4.

There are still over 100 miles of the fire's perimeter that are yet to be secured with fire lines. However, officials say they're getting a handle on the fire.

"We're pretty comfortable," Bierce said. "The lines aren't 100 percent, yet. The threat has lessened, but it's still there."

Times-News staff writer Matt Christensen welcomes comments at 735-3243 and at matt.christensen@lee.net.

Disaster Emergency County commissioners asked for and Gov. Butch Otter approved a disaster emergency for Cassia, Idaho, Nez Perce, Owyhee and Twin Falls counties. Disaster declarations authorize the use of state agencies to assist with the counties for the next 30 days unless terminated, changed or extended. Twin Falls County commissioners also approved an emergency ordinance banning open burning in the county. Offenders face a $1,000 fine and or up to three months in jail