A lightning-caused fire in the Bob Marshall Wilderness grew to 1,375 acres on Saturday.
The Damnation Fire was at 150 acres Friday before active burning in the Damnation and Lewis creek drainages increased its size.
The fire, approximately 21 miles east of Swan Lake, is burning primarily in previously burned areas, particularly the area burned by the Lewis Fire in 2000.
As the fire moved toward the Mud Lake Lookout, retardant was dropped around the lookout.
Structure protection efforts are underway on the Salmon Forks Cabin and sprinklers have been placed on the Big Salmon Bridge.
The fire has prompted the closure of the Helen Creek Trail, Trail in the Mist and Hodag Creek Trail.
The Damnation Fire is one of four fires believed to have been ignited by lightning on Aug. 11.
Two of the fires are about one-quarter acre while the Snow Creek Fire on the west side of the South Fork of the Flathead River has covered 34 acres.