Deep snow drifted into more than two dozen narrow ravines in the mountainsides – known as avalanche chutes – raising the danger of potentially deadly snow slides cascading onto I-70.
High winds and blowing snow forced the state to close the highway overnight. There was no word on when the busy thoroughfare through the mountains would reopen.
"I can't even venture a guess right now," Rod Mead, a spokesman for the Colorado Department of Transportation, said Monday.
Crews planned to use low-power explosives Monday morning trying to bring the snow down while the highway was closed, Mead said.
In addition to the avalanche threat, wind-blown snow reduced visibility to nearly zero.
At the 1.7-mile-long Eisenhower Tunnel about 40 miles west of Denver, wind gusts reached 70 mph, keeping crews from clearing the avalanche chutes.
"That is basically the problem we are having right now," said John Nelson, another spokesman for the transportation department. "It's not snowing, it's blowing snow."
P.J. Bailey left Breckenridge to head home on I-70 to Denver around 1 p.m. Sunday, but by nearly four hours later she was no farther than Georgetown, about 35 miles from Breckenridge.
"I was told it would get better, but a mile east of Georgetown, there were whiteout conditions. You couldn't even see the front of your car," said Bailey, 24.
She made her way back to Georgetown for the night.
"You should see this town. There's people stopped everywhere," she said.
Red Cross spokeswoman Melinda Epp said the agency opened seven shelters in schools and recreation centers and most of the 2,000-plus travelers who used them during the night were still there Monday morning. Others relied on the kindness of strangers.
Brian Jerry of Colorado Springs said strangers let him stay in their Silverthorne home Sunday night because motels were full.
"We called the local Quality Inn, and they basically laughed at us," Jerry said Monday.
Jerry, who had been snowboarding at Keystone Resort Sunday when high winds began, said he and his friends found a place to stay through conversations at a restaurant.
"The good will and the bonding together has been outstanding," he said.
Westbound I-70, the main route between Denver and many of the state's major ski resorts, was closed from 10 miles west of Denver to Vail, a distance of about 75 miles. Eastbound lanes were closed from Vail to Georgetown, about 60 miles.
It wasn't clear if the closures would hurt the ski resorts during the lucrative holiday season.
"It's going to be resort-by-resort," said Jennifer Rudolph, a spokeswoman for the industry group Colorado Ski Country USA.
The highway department also closed several other highways around the state Sunday as snow blown by wind gusting to 65 mph reduced visibility to near zero. U.S. 40 over Berthoud Pass, U.S. 6 over Loveland Pass and U.S. 550 over Red Mountain Pass all remained closed Monday.
Steamboat Ski Resort reported 17 inches of fresh snow Sunday.