The Grassy Ridge fire near St. Anthony, Idaho is 60,000 acres and is threatening structures.
The BLM says the fire was caused by lighting, after a storm Friday afternoon near Red Road.
BLM officials say the thunderstorm's winds caused the fire to spread, and describe the fire as "running and very active." Several hundred head of cows have died, but no humans have been injured. No evacuations are currently in place.
As of now, there is no estimated containment.