Denver ? Crews triggered avalanches Sunday before they could pose a threat to traffic on a mountain highway, a day after a huge snow slide knocked two cars off the road in a high pass and buried them.

Eight people had to be rescued from the cars, which were swept off the main highway to one of the state’s largest ski areas Saturday.

Wind whistled through the mountains west of Denver at 100 mph Sunday, producing whiteout conditions and driving wind chills well below zero, as artillery fire was used to set off controlled avalanches above the highway as well as at other mountain passes.

Witnesses said the slide Saturday morning pushed the cars down about 150 to 200 feet into trees off U.S. 40 near 11,307-foot Berthoud Pass, which leads to Winter Park Resort. The first sign of the avalanche was a puff of snow on the left side of the highway, said the driver of one of the buried cars.

“And it was just microseconds later that it hit us,” flipping his car over the roadside guard rail, Dave Boon of Fort Collins told KUSA-TV on Sunday.

“We started spinning and came to rest completely upside down buried in the snow,” said Boon, who dug his way out of the car and helped his wife out. He said they walked away with minor cuts and bruises.

Boon said the only things sticking out of the snow, which was at least 15 feet deep, were his car’s four wheels and suspension. “There was a tree about 20 feet above us, about 10 inches in diameter, that we snapped off. I think it is the only thing that kept us from going down the slope,” he said.

Members of Oakwood Road Church in Ames, Iowa, who were on a ski trip were among those swept away by the avalanche. Darren Johnson’s vehicle was the only one of the church’s four-car caravan hit by the snow, his father, Don, said.

The elder Johnson said his son was treated at a hospital and released, while a passenger in his car, Peter Olsen of Nevada and a sophomore at Iowa State University, was treated for a broken rib. Officials said Olsen was the only one still hospitalized Sunday.