The avalanche occurred in the backcountry south of Keystone Ski Area. Two skiers exited the ski area and descended into the North Fork of Swan River. Avalanches started in two locations and merged in a gully. The fatal avalanche occurred on an southeasterly aspect near treeline. It was 100 to 200 feet wide, and broke 4 feet to the ground. It funneled into the gully and ran about 2000 vertical feet. One skier was caught, partially buried, and self-rescued. The other was fully buried and killed. Their body was recovered on 2/11. "Sidecountry riders" exit ski areas to access backcountry terrain outside of operating ski area boundaries.