CUSTER COUNTY, Idaho (KLIX) – The Custer County Sheriff’s Office says a 23-year-old man from Pennsylvania was rescued at Mount Borah after his fall caused an avalanche.

Hao Yan of Devin, Pa., fell Saturday evening while climbing the north face of Mount Borah. His fall triggered a small avalanche, according to a news release, and the man called 911 while partially buried in snow about 11,500 feet, just below the north face access routes.

Yan was forced to remain on the snow field for about nine hours before rescuers could reach him. The Custer County Search and Rescue, with the help from a Montana helicopter team, reached Yan early Sunday morning.

Yan was flown to an ambulance and treated for severe hypothermia, the news release said. He was taken to the Lost River Medical Center, and then flown to Eastern Idaho Regional Medical Center.

At 12,657 feet, Mount Borah is Idaho's tallest mountain and a popular venue for climbers.