Eight backcountry skiers were killed in the deadliest avalanche in state history Tuesday in the Sierra Nevada mountains near Truckee, authorities said.

Six skiers — one guide and five participants in a three-day backcountry ski expedition — were rescued alive Tuesday, said Nevada County Sheriff Shannan Moon at a press conference Wednesday morning.

One additional skier remains missing, but operations have shifted from rescue to recovery, Moon said. The deceased skiers include five men and four women.

The 15 skiers were caught in an avalanche Tuesday near Castle Peak while returning to the trailhead after a backcountry ski trip. The avalanche occurred north of Interstate 80 near Donner Summit.

“Due to the ongoing challenges of the weather — the avalanche conditions — the effort remains ongoing, as well as our search for the remaining skier,” Moon said. “But the weather is a factor.”

Finishing a three-day trip with Blackbird Mountain Guides, the skiers had been returning from the Frog Lake Huts near the Castle Peak trailhead close to Interstate 80, an area that is prone to avalanche hazards. Castle Peak is located near Donner Summit heading into Truckee.

“It’s a very remote, rugged area on the north side of the highway there,” Moon said. “It is not a groomed area or a ski resort area.”

The group was made up of four guides and 11 guests, Moon said. Initial reports indicated that there had been 12 guests, but one attendee canceled their trip last minute.

A 911 call came into the Nevada County dispatch center reporting the avalanche around 11:30 a.m. Tuesday, Moon said. The group of skiers were on the third day of their expedition and were returning to the trail head at the time of the avalanche.

Initial reports Tuesday indicated that between seven and 10 people had been buried in the avalanche. The total number of skiers buried was later revised to 15, according to the Nevada County Sheriff’s Office. Six skiers had been rescued by Tuesday night, two of whom were transported to a hospital for treatment.

The Nevada County Sheriff’s Office organized a joint response with assistance from the Placer County Sheriff’s Office, the Tahoe Nordic search and rescue team and the Washoe County Sheriff’s Office and search and rescue team, Moon said. The mutual aid effort was coordinated through the California Office of Emergency Services.

On Tuesday, around 50 “highly skilled” rescuers embarked from Boreal Mountain Ski Resort and the Tahoe Donner Alder Creek Adventure Center amid the difficult weather conditions, Moon said. Those conditions — plus remaining “very high” avalanche danger — posed difficulties in the transportation of rescuers and rescue equipment. The rescue teams were sent into the field with “lots of safety plans.”

“Extreme weather conditions, I would say is an understatement. Lots of snow, gale force winds making it impossible to see,” Moon said. “It was very much a slow and steady pace.”

Before arriving at the scene, the rescue teams were aware that six skiers had survived and were in communication with them via iPhone’s SOS feature. Rescuers traveled on a Snowcat to about two miles away from the site, when they had to then ski the rest of the way in due to concerns of another avalanche.

Rescuers were able to make it to the scene around 5:30 p.m., Moon said. They recovered the six survivors, two of whom were not mobile due to injuries they sustained in the avalanche.

While waiting for rescuers, the group of survivors began their own search for their missing trip mates and located three deceased skiers, Moon added.

The survivors include one man and five women and range in age from 30 to 55, Moon said.. Of two survivors taken to the hospital, both suffered non-life threatening injuries. One was treated and released Tuesday night, and the other remains there receiving treatment.

Moon added that this remains an ongoing incident and facts may continue to change.

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