Eight backcountry skiers were found dead and one remains missing and presumed dead after a massive avalanche near Lake Tahoe, authorities said Wednesday, marking the deadliest avalanche in the United States in more than four decades.

The avalanche struck Tuesday morning in the Castle Peak area of the Sierra Nevada, northwest of Lake Tahoe, burying a group of skiers on a guided three-day trek.

According to the Nevada County Sheriff's Office, the eight victims were located fairly close together. Among them were three of the four guides leading the expedition. The fourth guide survived.

Six other skiers from the group were rescued alive Tuesday. One remained hospitalized Wednesday.

The group included men and women between the ages of 30 and 55. Authorities have not yet released the names of the deceased, pending notification of families.

“They’re still reeling,” Nevada County Sheriff Shannan Moon said. “I could not imagine what they’re going through.”

Capt. Russell Greene of the sheriff’s office said someone in the group saw the avalanche coming and shouted a warning, but it overtook them quickly.

Treacherous Rescue Effort

Search and rescue crews were dispatched after a 911 call reported that 15 skiers had been buried. Heavy snowfall, gale-force winds and the continued threat of additional avalanches hampered recovery efforts. Crews have not yet been able to remove the victims from the mountain due to extreme conditions.

The avalanche occurred near Castle Peak, a 2,777-metre mountain north of Donner Summit, a popular but challenging backcountry skiing destination. The region is among the snowiest in the Western Hemisphere, receiving nearly 10 metres of snow annually, according to the Truckee Donner Land Trust, which owns huts near Frog Lake where the group had been staying.

The Sierra Avalanche Center warned Wednesday that avalanche danger remains high. Multiple metres of recent snowfall combined with strong winds have left the snowpack unstable, with more snow forecast.

Authorities said they were alerted by Blackbird Mountain Guides, which was leading the trip, as well as by emergency locator beacons carried by the skiers.

In a statement, Blackbird Mountain Guides said the group was returning to the trailhead on the final day of the excursion when the avalanche struck. The company said it is cooperating fully with authorities.

Deadliest Since 1981

The tragedy is the deadliest avalanche in the U.S. since 1981, when 11 climbers were killed on Mount Rainier in Washington state.

Avalanches kill an average of 25 to 30 people each winter in the United States, according to the National Avalanche Center.

Several ski resorts in the Lake Tahoe area were fully or partially closed due to the storm. Experts noted that controlled ski resorts, which use explosives and barriers to mitigate avalanche risks, are generally less hazardous than backcountry terrain.

Officials said search operations would continue as weather conditions permit.