COOKE CITY — An 18-year-old Minnesota man has died after he was buried in an avalanche in southwestern Montana that may have been triggered by another rider.

The victim was stuck on a slope and trying to start his snowmobile Tuesday afternoon and another snowmobiler was riding above him on the mountain when the avalanche was triggered. The Gallatin National Forest Avalanche Center continued to investigate the cause of the slide on Wednesday.

The Park County sheriff's office received a report of a snowmobiler buried in the Daisy Pass and Crown Butte area near Cooke City about 4 p.m. Tuesday.

The victim, from Lake Lillian, Minn., was found under about 6 feet of snow shortly after 5 p.m., more than two hours after he was buried. His name hasn't been released.

The avalanche center estimates the avalanche was 500 feet wide, 600 feet long and up to 20 feet deep in places.

None of the seven snowmobilers in the party had avalanche beacons, avalanche center officials said.

Undersheriff Scott Hamilton says one other member of the party was knocked off his snowmobile but not buried. He was slightly injured.

"Avalanche conditions are extreme throughout the entire region," Hamilton said. "Snowmobilers and skiers are cautioned to be mindful of these conditions and avoid areas prone to sliding."

The man is the fifth Montana avalanche victim since Jan. 1. Twenty-three people have died in avalanches nationwide since Dec. 26, according to the Colorado Avalanche Information Center.