A thousand tons of rock that broke from a mountainside on McClure Pass near Paonia on Monday have signaled the annual spring rockfall season is open on Colorado’s highways.
The rock, including several chunks the size of vehicles, tumbled onto Colorado 133 at 5 p.m. and damaged the roadbed and guardrail about 16 miles north of Paonia and directly across from the Paonia Reservoir dam. The rock slide did not hurt anyone and no vehicles were hit.
“That stretch of road has had rockfall events before and they will happen again,” said Matt Sares of the Colorado Geological Survey.
The Geological Survey works with the Colorado Department of Transportation on stabilizing and clearing rock. Problems with rock faces crumbling apart tend to happen more often this time of year because repeated thawing and freezing over the winter causes a heaving that erodes shale and loosens chunks of sandstone, Sares said.
Highway crews cleared some of the rock from McClure on Monday evening and allowed some waiting vehicles to pass through the area. The road was closed Tuesday while the damage could be assessed and the larger rocks could be blasted apart. One lane was opened to traffic Tuesday evening, and motorists should expect possible half-hour delays through Friday while road crews scale other loose rock and patch up the road.
“Our rockfall geologists are paying attention to problem areas and monitoring them,” said CDOT spokeswoman Nancy Shanks.
The department also has been designing rockfall mitigation measures into newer highway improvement projects, including Snowmass Canyon near Aspen and Glenwood Canyon east of Glenwood Springs. Currently, the department is doing a major scaling, bolting and wire-mesh mitigation project on Colorado 550 on Red Mountain Pass north of Silverton.
“But it’s not something we can prevent 100 percent,” Shanks said.
Staff writer Nancy Lofholm can be reached at 970-256-1957 or nlofholm@denverpost.com.
