HAMILTON, Mont. -

A 55-acre wildland fire burning in Lost Horse Canyon between Hamilton and Darby has helped prompt Ravalli County to enact a Stage 1 fire alert.

County commissioners voted to ban open burning after meeting with Forest Service, sheriff's, fire and emergency officials Monday morning.

Besides the open burning ban, incendiary devices are prohibited and campfires must be in contained areas.

The Forest Service also restricted camping on Lost Horse Road all the way to Twin Lakes, to day use only.

"Aside from the fact that it's such a popular, busy canyon, and it's one way in, one way out access," said Forest Service District Ranger Chuck Oliver, "we are watching that very closely. We will end up closing Lost Horse Canyon at some point if the fire continues to persist as it is, and there's no indication that it won't continue to move in the direction that it is moving."

The fire is burning in steep, rugged terrain and has moved to the north and east.

Infrared has found that the fire has burned 55 acres. That's up from 40 acres over the weekend.

The Forest Service tells us infrared offers a more accurate assessment, so it's not entirely certain that the fire grew by 15 acres.

The lightning-caused fire is not threatening any structures at this time, and cooler weather Monday proved valuable.

Helicopters had been dropping water and retardant on the fire over the weekend. No ground crews can gain access in the steep, dangerous, rocky terrain.

If the fire grew out of control it could push toward the Highway 93 corridor.

NBC Montana met up with a Type 2 fire incident team that had arrived Monday morning. They were from the Sequoia National Forest in California, and had been fighting fire in Utah. The team will act as fire scouts in the Lost Horse drainage.

Mary Wojciechowski lives in the Lost Horse Road area. The fire is burning 8 to 10 miles from her house.

Just in case, Wojciechowski said she has called a friend to make room for her and her animals, if there is a need to evacuate. She has two dogs and a cat.

"I know it can just tear down the drainage," said Mary, "so once I heard about the fire it's that immediate OK, what do I need to get out if I have to."

Up on Coyote Coulee the mountains at noon on Monday, were free of smoke. By late afternoon, you could see a couple smoke plumes in the distance from Darby.

Lost Horse has always been a prime huckleberry picking area.

Ethel Harris has been picking in Lost Horse since she was a kid, and on Monday, her work proved bountiful. But she was keeping close watch on the fire.

"I am, because it grew yesterday," said Ethel. "It grew the day before and now we've got 90-degree weather."

The Forest Service told NBC Montana it is a difficult fire to fight, with boulders the size of vehicles in the terrain.

Lost Horse has also not seen a major fire for decades, so fuel is plentiful, and pine beetle kills have taken their toll on may trees here.