A rock slide punched gaping holes in a bridge and left huge boulders on Interstate 70, closing a 17-mile stretch of the highway in western Colorado.
The slide struck around midnight Sunday near Hanging Lake Tunnel in Glenwood Canyon, a deep, narrow chasm about 110 miles west of Denver, the Colorado Department of Transportation said.
No injuries or damage to vehicles were reported.
All lanes were closed from Glenwood Springs east to the town of Dotsero. Up to 25,000 vehicles a day travel that section of highway, department spokeswoman Stacy Stegman said.
The slide blocked the main route between the Denver airport and the Aspen Skiing Co.'s four Aspen-area resorts, but company spokeswoman Meredith McKee said resort operations weren't disrupted.
Officials haven't determined how long the highway will be closed. Because of the rugged terrain, the shortest detour adds about 200 miles around the mountainous Flat Tops Wilderness Area.
The largest hole in the roadway was 10 feet by 20 feet. About 20 boulders ranging from three to 10 feet long were scattered on the highway, with the largest weighing 66 tons, officials said.
Crews began drilling holes in the boulders to insert explosives and blast them into smaller pieces to be hauled away.
Some lanes could then be reopened, but Stegman didn't know how long it would take to finish roadway repairs and reopen all the lanes. The westbound lanes were the most badly damaged.
A 1995 rock slide on I-70 in Glenwood Canyon killed three people.
A slide on Thanksgiving Day in 2004 closed the highway and required nearly $700,000 worth of repairs. No one was hurt because the highway had previously been closed for an unrelated crash.
The Union Pacific Railroad said its tracks through the canyon weren't affected. The tracks carry freight trains and Amtrak's California Zephyr.
Monday editions of the Glenwood Springs Post Independent and the Aspen Times were delivered late because the slide struck between their towns and their printing plant in the town of Gypsum.