A road collapse north of New Underwood is complicating travel on an important western South Dakota connection between Interstate 90 and Highway 34.
The problem for Meade County Highway Superintendent Ken McGirr begins with the soil. It just doesn't like to stay put.
"Laymen's terms, a blue shale," McGirr said. "It's a crunchy soil that swells when it's wet, shrinks when it's dry and it's slippery."
That slippery swelling and crusty shrinking means instability. The signs are all over the surrounding Belle Fourche River breaks. Add a wet year and pretty soon a big chunk of the New Underwood Road was heading downhill.
When it started to shift, McGirr had his highway crews build a detour -- just in time.
"We moved the traffic off just in case it would fail," McGirr said. "The next morning we found the road down about eight inches, 10 inches. The following day down another foot. The following day down another foot."
Within a few days, a 40-foot-long section of the highway had fallen away, leaving a jagged drop-off from the asphalt up to ten feet deep in places.
As a short-term solution, this detour is going to work just fine. The long-term fix, however, will be a lot more complicated.
That won't come until next summer, at least. And it will likely mean moving the road to more stable ground nearby, an expensive option with creative engineering demands.
But the county must keep the highway open, McGirr said.
"It's the only asphalt connection between Sturgis and Phillip to come down off the north from Highway 34," McGirr said. "So it's absolutely a major connector that's maintained by the county."
All in a landscape where movement matters -- both above and beneath the asphalt.
McGirr says the New Underwood Road handled about 800 vehicles a day before the slide. They include residents of the Cheyenne River going to and from Rapid City, local ranchers and vehicles going to and from the oil fields of North Dakota.