Crews doing rockfall work on U.S. Highway 550 at Bondad brought down about 10 large slabs of rock weighing between 500 and 1,000 pounds each, but the largest chunk of all remained stubbornly lodged Tuesday afternoon.

This means the work will continue today, forcing travel down to one lane in each direction and causing intermittent closures, said Kent Baxstrom, a maintenance supervisor with the Colorado Department of Transportation.

If wedging air bags in cracks of the slab, estimated to weigh about 20 tons, doesn’t work, they’ll use explosives, Baxstrom said.

The work should be done by this evening, he said.

The section at Bondad Hill is a persistent threat for rockfall, especially in the spring during frequent freezing and thawing.

Baxstrom said rock chunks commonly come down on their own but haven’t hurt anybody in recent memory.

Alan Hotchkiss, a senior geologist with the Colorado Department of Transportation, said the Mancos Shale that underlies the sandstone makes a weak base.

Katie Burford