The springtime freeze and thaw cycle has descended upon Routt County, which has caused rocks and boulders to fall on local roads. As temperatures begin to warm up, the Colorado Department of Transportation is urging drivers to keep their heads up for rocks falling down. 

Coming out of a winter with heavy precipitation, canyons outside of Hayden and Milner — historically prone to landslides — have already seen their fair share of road closures due to falling rocks. 

CDOT said Mount Harris Canyon and two different stretches of U.S. Highway 40 in Routt County — one east of the Yampa Valley Regional Airport (mile marker 113.7) and one just west of Milner (mile marker 119.5) — have kept their hands full with rock removals this spring. 

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CDOT’s Northwest Regional Communications Manager Elise Thatcher said the agency responds to Mount Harris Canyon one to three times a week for rockfall in the area. This includes the March 15 accident involving a Dodge pickup crashing into a ditch after swerving to miss a rock near Mount Harris Canyon. 

Mount Harris Canyon and the two other problem sites have long been susceptible to landslides in years that brought lots of snow, and more so than other areas of Colorado. What makes these places in Hayden and Milner more prone to rock fall events? The short answer is coal.

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The presence of coal in Routt County causes the rocks in the area’s canyons to be less dense and more likely to break off from the structures they are attached to.

Professor of Geological Sciences at the University of Colorado Boulder Lon Abbott explained that millions of years ago, before the Steamboat, Hayden and Craig area was dominated by mountains, it was marshland. 

The marshland environment caused the mountains that formed in the area to have more mud and coal in comparison to many of the mountains across the rest of the state, which have more sand. Stone made from mud and coal, or mudstone, is less dense and sturdy than stone that comes from sand, or sandstone. 

According to Abbott, mudstones are easily eroded, but if they are capped by one of the sandstones — which is the case in the area’s canyons — the sandstone protects them from eroding. However, the capping sandstone can’t always withstand springs that follow heavy precipitation winters. 

“When you get a wet year, you get a lot of sediment that is moving down the slope, the mudstone gets eroded really quickly and it will undercut the sandstone and the blocks of sandstone tumbles down the hill slope,” Abbott said. 

To prevent rocks from making it all the way down the slope and into the road, CDOT will place rockfall fencing made by mesh netting along the roads. The issue with Mount Harris Canyon, according to CDOT statistics, is rocks make it past this fencing an average of three to five times a year. 

“Crews clear out the rocks from the ditch next to the fencing one or two times a year. That way the fencing can help catch more rocks,” Thatcher said. 

Thatcher indicated that the moment CDOT becomes aware of a situation where a rock makes its way into the road, the agency will dispatch workers immediately. Once on scene, CDOT takes whatever action necessary to ensure all lanes of the road stay open. This generally involves quickly moving rocks or related debris to the side of the road and coming back later to relocate it. 

As a preventative measure, CDOT also employs a method called scaling in which rocks that appear to have the potential to fall off the canyon walls are forcibly removed. Thatcher said CDOT has plans to perform rock scaling in the location east of the airport in the near future. 

“Our Geotech team will survey the rocky areas next to this section of U.S. 40 later this spring because we are considering putting in a higher barrier at this location along the highway,” Thatcher said. 

According to Thatcher, more information and review is needed by the Geotech team in order to move forward with this process. 

Thatcher emphasized the importance of being alert while driving and being off one’s cellphones in order to read signs that indicate problematic rockfall areas are ahead.