Second, where the road enters and leaves roadcuts, buckling of the pavement occurs at the transition from fresh shale at the bottom of the cut to weathered shale on the old slope and between the weathered shale and the compacted fill of the roadway. Third, in open areas, the pavement may buckle at zones of minor faulting where water saturates the subgrade each season. Fault zones may be indicated by changes in vegetation in borrow pits or adjacent fields. Fourth, the Pierre shale is very unstable on steep slopes, and surface creep and landslides are common. Most earth movements occur in the spring when the surface shales are saturated with water.
Landslides are common along highways built on steep hillsides.
The lower edge of the grade frequently fails, and entire sections of highway may move downslope overnight. Even the life of concrete structures may be seriously shortened if they are in contact with the more corrosive parts of the Pierre shale. Again, geology is a major factor that must be evaluated in order for the EIS to be complete.