A pair of snowmobilers were killed Monday when they were buried in a large avalanche north of Cooke City, Montana.

Carl Thelen, 39, and Jesse Thelen, 43, both of Minnesota, were part of a group of eight people who’d been snowmobiling on Scotch Bonnet Mountain, according to reports from law enforcement and media outlets.

The group was on its second day of riding in the area, according to Ian Hoyer of the Gallatin National Forest Avalanche Center. After spending their first day riding in the flats and in the trees, Scotch Bonnet Mountain was the first slope they attempted to climb, Hoyer said, and two of the snowmobilers got stuck. Two other members of the group rode up to assist, Hoyer said, but “while they were working to get the snowmobiles unstuck, the avalanche was triggered and broke, came down [and] caught two of the riders.”

According to media reports, those riders were Carl and Jesse Thelen.

The other six members of the group activated their rescue beacons, found the two men and dug them out, but were unable to save their lives.

“Our deepest condolences go out to the victim’s friends and family, members of the group and the search and rescue community,” the Friends of the Gallatin National Forest Avalanche Center said in a Facebook post.

According to Hoyer, the avalanche broke 4-5 feet deep, underneath wind-drifted snow that had fallen in the past two weeks.

“It was just a big loading event,” he said. “All that new snow fell onto weak snow near the ground.”

When the weak layer collapsed during Monday’s incident, it released an avalanche about 300 feet in width which flowed about 500 feet down the slope and piled up 8 to 9 feet deep, Hoyer said.

The Bozeman-based avalanche center said multiple feet of snow had fallen amid windy conditions in recent days, creating “unstable conditions” across the region.

On Monday morning, ahead of the fatal accident on Scotch Bonnet Mountain, the center warned of dangerous conditions in the mountains around Cooke City, West Yellowstone and in the Southern Madison and Southern Gallatin ranges.

“Human-triggered avalanches are likely on steep wind-loaded slopes and large avalanches could break deeply on buried weak layers,” the center warned. “Avoid recently wind-loaded terrain and carefully assess the snowpack and terrain prior to approaching steep non-wind-loaded slopes.”

Following Monday’s deaths, the center further warned that the same conditions that resulted in the avalanches in Cooke City still exist in the region’s mountains.

“The wind is still loading slopes and it is likely a skier or rider could trigger a large avalanche. It is best to avoid these slopes,” the center said Wednesday. “They will be found near ridgelines, above treeline, and in gullies.”

The center added that signs of wind-loading include “cornices, smooth pillows of dense snow and shooting cracks — a bullseye sign of instability.”

Monday wound up being a busy day for first responders in the Cooke City area.

Two other snowmobilers, also from Minnesota, were reported as overdue that day, and Park County, Montana, Sheriff’s Office Search and Rescue members were initially unable to find them. However, the individuals were safely located on Tuesday, “after unintentionally spending the night out,” said Sheriff’s Cpt. Tad Dykstra.

“Please remember to always check the avalanche report and assess current local conditions before riding in avalanche terrain,” Dykstra said in a statement.