DENVER -- Crews working to reopen a 17-mile stretch of Interstate 70 in western Colorado where a rock slide left behind gaping holes and huge boulders on a bridge were carrying out a plan Tuesday to mitigate another loose boulder on the hillside above.

Highway crews hiked up the side of the canyon near the Hanging Lake Tunnel to begin rock scaling -- removing loose rocks from above.

CDOT geologists have determined that a large rock above the highway is too unstable to remain in place.

"They will start scaling above the unstable rock and work towards it with the goal of prying it loose and/or gaining a better understanding of its stability," said Mindy Crane, a spokeswoman for the Colorado Department of Transportation.

The slide struck around midnight Sunday in Glenwood Canyon, a deep, narrow chasm about 110 miles west of Denver, prompting Gov. Bill Ritter to declare a disaster emergency.

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 the major east-west artery, CDOT spokeswoman Stacey Stegman said.

Because of the rugged terrain, the shortest detour adds about 200 miles around the mountainous Flat Tops Wilderness Area.

Stegman said the rock slide took out median barriers, steel guardrails and at least one lightpole.

"To me, it looks like a war zone," she said. She said that from an engineering perspective, though, the damage was less than originally thought.

Ritter's disaster declaration for the highway allows the state to seek funding from the Federal Highway Administration to help pay for repairs.

The largest hole in the roadway was 10 by 20 feet in the westbound lane. About 20 boulders ranging from three to 10 feet long were scattered on the highway, with the largest weighing 66 tons, officials said.

Crews drilled holes in the large boulders to insert explosives and blast them into smaller pieces. Stegman said once the crew clears the debris, they will be able to find out which lanes can reopen.

Transportation officials don't know yet how long it will take to finish roadway repairs and open all the lanes. Typically, they work to reopen one lane of one direction of the roadway and then allow alternating traffic while the more seriously-damaged portions undergo repair.

A 1995 rock slide on I-70 in Glenwood Canyon killed a mother and her two sons from Aspen. 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.