The sun was shining Saturday morning in Salt Lake City — a beautiful day, local officials said, that masked a hidden danger.

Four skiers in their 20s and 30s were killed in one of the most deadly avalanches in the history of Utah.

Eight skiers from two different groups were on steep terrain in the Wilson Glade area of Mill Creek Canyon — about 9,800 feet high — when they unintentionally triggered the slide, the Utah Avalanche Center said in an accident report.

All eight skiers were buried. Four were able to dig themselves out; the other four died under the snow. The victims have not been publicly identified, but Drew Hardesty from the Utah Avalanche Center said they were well-known in the community, the Salt Lake Tribune reports.

After the survivors freed themselves, they dug out the remaining bodies, Sgt. Melody Cutler of the Unified Police Department of Greater Salt Lake told reporters. "They unburied themselves and then unburied their friends," she said.

The accident marked the most deadly avalanche in the state since a 1992 avalanche that also killed four.

"This is a terrible tragedy and our prayers go out to the victims and families involved," Gov. Spencer Cox tweeted. "We are grateful to the first responders and others who engaged in this rescue and recovery effort. With avalanche danger high right now, please exercise extreme caution."

Forecasters had warned skiers of a high avalanche risk in the area. "High Danger," the Utah Avalanche Center tweeted hours before the slide. "Large natural avalanches overnight. Dangerous avalanche conditions."

The bottom layers of snow were weak, forecasters say. "Most slopes have persistent weak layers of faceted snow at the bottom half of the snowpack," the Utah Avalanche Center wrote in discussing conditions for nearby areas.

"New snow that fell in January formed a slab on top of these weak layers," the center wrote. "Imagine a building with a weak foundation but we keep adding additional floors on top - eventually the whole structure collapses."

Six people have now been killed by avalanches in the state this winter.

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