WHITEFISH, Mont.—A 54-year-old California man died while skiing with his son at Whitefish Mountain Resort in northwestern Montana.

The Flathead County Sheriff's office says the man's son found his father upside down in a tree well on Saturday, and that he couldn't be resuscitated.

Tree wells form at the base of trees and can be difficult to escape.

He's the third skier to die in a tree well at the resort since 2010. The family of a German foreign exchange student who died after falling in a tree well in 2010 filed a lawsuit against the resort last month.

State and federal officials are investigating the most recent death. The man's body has been sent to the state crime lab in Missoula for an autopsy.

The man's name hasn't been released.