Impassible when wet
I spent a total of 3 weeks along the ND-MT border in what's now National Grasslands,south of Theodore Roosevelt NP, in June-July 1975. We were on a dinosaur fossil excavation project and all of our 5 vehicles were 2 wheel drive. Our access road was "Old Highway 16" which ran, and still runs, north from Marmarth, ND up to Medora, Golva, and Beach, ND. The dig was in part in the ditch along this "main road". We had an unseasonable system of thunderstorms provide us with 2 days of rain. It took the public road 3 days to become drivable again, and even then it was snotty.
The badlands in both western ND and SD are made up primarily of volcanic ash. They weather to highly expanding and water-absorbing gumbo clay, so when they get heavy rain, not much moves. As the storm system approached, a rancher who lived nearby (near in western ND terms--about 10 miles from the dig), came by and implored us not to drive on the road until it was dry, as the ruts cut by those driving too soon could only be repaired by grading the whole length of the road. He made it clear that he, other ranchers, and the Slope County Roads supervisor would be highly annoyed if we cut their roads up.
"Impassible when wet" is real-world in the badlands underlain by the Hell Creek Formation's ash beds.
Foy
