GLENWOOD SPRINGS, Colo. (AP) — Workers hiked up the side of a Colorado canyon Tuesday to examine another boulder threatening to fall on Interstate 70 after a rock slide forced the highway to close indefinitely.

The rock under scrutiny is about 20 feet in diameter and sits about 900 feet above the roadway, the Colorado Department of Transportation said.

After ascending the canyon wall, the crew began working its way back down a steeper section with climbing ropes to reach the boulder.

They will decide whether to pry it loose or break it up so it falls in smaller pieces, department spokeswoman Mindy Crane said.

Officials were still waiting to hear at mid-afternoon Tuesday what the crews planned to do.

About 20 boulders tumbled onto I-70 in Glenwood Canyon at about midnight Sunday.

No injuries or damage to vehicles were reported, but the slide left holes as large as 10 feet by 20 feet in a bridge-like elevated section of roadway.

Crews were breaking up the fallen boulders with explosives so they could be hauled away.

A 17-mile stretch of I-70 is closed in Glenwood Canyon from Glenwood Springs to Dotsero. Crane said the department still has no estimate of when it will reopen.

I-70 is a vital east-west link in Colorado, with up to 25,000 vehicles a day traveling through the canyon. The shortest detour is more than 200 miles.

Gov. Bill Ritter declared a disaster emergency for the highway, allowing the state to seek funding from the Federal Highway Administration to help pay for repairs.

Engineers are still developing an estimate of the repair costs. A similar slide in the same area in 2004 cost $1.2 million to repair, including a $700,000 emergency contract with a contractor.

Arthur Daily, of Aspen, who was injured in a 1995 rock slide that killed his wife and two children near the same location, said he drove past the site about 90 minutes before the rocks fell again last weekend.

“I just thought, thank God that there was nobody in that part of the canyon when the rocks fell,” Daily told the Aspen Times. “That could have been a very tragic event.”

Cottonwood Pass not an option A statement provided by Eagle County addressed questions concerning Cottonwood Pass. The closure of Interstate 70 through Glenwood Canyon generated several requests that Eagle County open Cottonwood Pass to through traffic. While it does appear on local maps, the gravel road is not maintained for winter travel. According to Brad Higgins, Eagle County's director of Road and Bridge, Cottonwood Pass, which connects Gypsum to Cattle Creek south of Glenwood Springs, closes every winter from the end of November until mid-April. “Cottonwood Pass has never been maintained in the winter, nor is it designed to handle a high volume of vehicles, so to simply open it to traffic is not an option,” said Higgins. “Ice and snow accumulate on the sides of the road and create large ruts, making it impassable for regular passenger vehicles or tractor-trailers as well as making it too narrow for two-way traffic.” Snow slide on railroad tracks Railroad authorities reported that although the rock fall near Hanging Lake did not affect their rail corridor, a snow slide near the eastern end of the canyon on Monday did cover the tracks. Mark Davis, a spokesman for the Union Pacific Rail Road, owner of the tracks, said it was unknown as of around 4:30 p.m. when the track might be cleared. He said the railroad emergency management crews were just being dispatched to the scene to check out the slide.

Slideshow of rock fall aftermath and cleanup

CDOT's UPDATE 8:30 AM, MARCH 9 Crews have begun their hike up the hillside in Glenwood Canyon and will begin rock scaling by around 10:00 A.M. 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. The rock is approximately 20 feet in diameter.