A snowmobiler who died in an avalanche Jan. 5 near Choteau was not wearing an avalanche beacon, according to information in a preliminary report from the Flathead Avalanche Center.

The fatal avalanche occurred in Waldron Creek west of Choteau on the Flathead National Forest just beyond the Teton Pass Ski Area.

According to the report, the avalanche was unintentionally triggered by a snowmobiler, and was large enough to “destroy a car or wood frame house,” the report said.

“Two riders were caught, one was injured and one buried 2 feet deep. Unfortunately, the buried rider was not wearing a beacon and did not survive.”

The snowpack failed 1 to 5 feet deep on a weak layer near the ground.

Also on Saturday, a man riding a motorized snow bike was seriously injured after being swept by an avalanche off a cliff at the top of Spring Slide Mountain in the southern Swan Range.

According a preliminary report from the Flathead Avalanche Center, the group of motorized snow bikers was stopped on top of the peak to take pictures and check maps. A large cornice broke beneath one of the riders.

“The cornice subsequently triggered several thick slab avalanches in very steep, rocky and cliffy terrain,” the report stated. “These appear to be persistent slabs.”

The rider fell 200 feet over cliff bands and was carried another 100 feet down the slope and buried. His partners were able to dig him out, but he suffered numerous serious injuries from the fall.

Two Bear Air evacuated the victim and he was recovering from surgery on Sunday.

Avalanche danger was rated as considerable above 5,000 feet across the forecast area on Monday. Careful snowpack evaluation, cautious route-finding and conservative decision-making essential, the avalanche center warned.

Monday’s avalanche reported stated that persistent slab avalanches remain a problem.

“They are a low probability high consequence problem as was unfortunately illustrated with the recent avalanche fatality outside of Choteau.”