A dusting of snow this week in the high country above Durango is a reminder of the approaching freeze-thaw cycle that tends to loosen rocks along area highways.
One such rockfall occurred Tuesday between Coal Bank and Molas passes on U.S. Highway 550 south of Silverton. A minivan hit a rock about 7 p.m., which caused minor damage to the minivan, according to the Colorado State Patrol.
The freezing temperatures cause water between the rocks to expand, which loosens boulders. The process is repeated with the warming days and freezing nights.
Monsoon rains also loosen rocks and can send mud and debris washing over roads. The Colorado Department of Transportation has a 10-person crew and six pieces of heavy equipment improving a section of Colorado Highway 145 west of Telluride where mud and debris filled culverts and ran across the road.
Motorists were advised to expect intermittent delays from 8 a.m. until 5 p.m. Monday through Friday for the next two weeks.
The Durango area has several problem areas when it comes to rockfall, including Colorado Highway 3 and Bondad Hill.
Crews performed mitigation this summer in both locations, but more needs to be done at the top of Bondad Hill, where a couple of bus-sized boulders have landed on U.S. Highway 550, said Lisa Schwantes, spokeswoman with CDOT.
The highway department also did rock mitigation on U.S. Highway 160 between Durango and Pagosa Springs, including clearing debris and installing new mesh material that captures boulders before they fall onto the road, she said.