Survivors of a Colorado avalanche recalled being tossed around by a massive snow slide that buried two cars as crews on Sunday fired artillery shells to safely set off avalanches to protect traffic from other possible threats.

"We started spinning and came to rest completely upside-down buried in the snow," Dave Boone of Fort Collins said.

Crews fired artillery shells Sunday to safely trigger avalanches 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 that were swept off the main highway to one of the state's largest ski areas Saturday.

"It was actually pretty massive,” said Pete Feragin, who photographed the avalanche and used to live in a nearby cabin.

"It was pretty terrifying," he said. "To be inside of it would probably be some people’s worst nightmare."

Photo Essay: Avalanche

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

Witnesses said the slide on Saturday 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, Boone recalled.

"It kind of tilted the car and it was kind of like a freight train hit us and flipped us over the guard. It was hard to remember how many times," he told KUSA-TV on Sunday.

He dug his way out of the car and helped his wife out. He said they walked away with minor cuts and bruises.

Boone said the only thing sticking out of the snow, which was at least 15 feet deep, was 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, including Darren Johnson, said his father, Don Johnson.

Darren Johnson's vehicle was the only one of the church's four-car caravan hit by the snow, his father said.

Don 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.

The avalanche hit between 10 a.m. and 10:30 and was about 200 to 300 feet wide and 15 feet deep, State Patrolman Eric Wynn said. The area usually has slides only 2 to 3 feet deep because crews trigger them before more snow can accumulate, said Spencer Logan of the Colorado Avalanche Information Center.

Despite three snowstorms in as many weeks, the area of the avalanche hasn't been hit as hard as eastern parts of the state, which got up to 4 feet of snow, Logan said. But the pass did get up to 10 inches in the past few days, he said.

Logan blamed 30 mph wind, with gusts up to 60 mph Saturday morning, for the avalanche conditions.

Mile Cikara, who was headed to Winter Park to ski, told KMGH-TV in Denver that he joined others furiously digging out victims. "I along with 30 other people grabbed shovels and started digging to get people out. I had a shovel but people were using their hands, skis, ski poles, whatever, to dig out," until rescue teams arrived, he said.

The timing meant most traffic headed to the ski area had already passed through.

"Good thing it didn't happen a couple of hours earlier," said Darcy Morse, a Winter Park spokeswoman. On an average January weekend day, the resort draws more than 10,000 skiers and snowboarders, with lifts opening at 8:30 or 9 a.m.

The pass was closed after the avalanche but reopened Saturday night.

The Associated Press contributed to this report.