JACKSON, Wyo. (AP) — Authorities have determined that the unusual snowmobile wreck in northwest Wyoming that killed a 33-year-old North Dakota man was an accident.

Andrew Grossnickle, of West Fargo, died Dec. 30 after becoming separated from his snow machine. A preliminary autopsy determined that Grossnickle died from blunt force trauma to the left chest.

Investigators were perplexed initially because the snowmobile was not damaged.

Typically, fatal snowmobile accidents involve the machine crashing into a tree or rolling over the victim.

But Teton County Sheriff's Lt. Slade Ross says it appears that Grossnickle fell off the machine or contacted a tree while hanging off the snowmobile.

Grossnickle was among a group of eight friends but no one saw the accident.