One survivor tried but couldn’t save his girlfriend.

Due to a shallow snowpack, slide conditions had been extremely unstable in recent weeks in the Wasatch Mountains, especially on Feb. 6, the day after a storm left at least a foot of dense powder.

“They thought any avalanches in that area would be ‘pockety,’ and did not think the entire slope would avalanche as it did,” states the report.

The skiers were ascending a “skin track” in two widely spaced groups when a 3.5-foot thick “hard slab” broke loose above them across 1,000 feet of Wilson Peak’s northeast face, according to the report.

“This avalanche was likely human triggered, but it cannot be determined by whom,” it states. Both groups adhered to standard practices for staying safe in slide-prone backcountry and most of the skiers were familiar with the terrain. Even so, four lives were lost in Utah’s deadliest avalanche since 1992.