Epigenetic Valley

a watergap valley whose direction is not related to the tectonic structure or the composition of the rocks that make up the ranges, ridges, and other forms traversed by the river. Epigenetic valleys result from the activity of rivers that had carved out their original valley in rocks of an earlier structural stage that were subsequently partially or completely eroded away. When the river cuts deeper into the rocks of the lower structural stage, the valley retains its initial direction, becoming a superimposed, or epigenetic, valley.