A backcountry avalanche warning is in effect for the mountains near Cooke City, just north of Yellowstone National Park.
The Gallatin National Forest Avalanche Center said Thursday that heavy snow and strong winds were creating dangerous conditions.
It has snowed 11 out of the past 12 days around Cooke City and the combination of snow and wind has "pushed many slopes past their breaking point," the center's advisory said.
The area received up to a foot (30 centimeters) of new snow between Wednesday morning and Thursday morning, making things more unstable. The avalanche danger is rated high on all slopes.