 As a result, substantial coulees and scablands were created in the Upper Crab Creek drainage, and the drainage below the Potholes Reservoir is overlarge (i.e., the channel sizes could contain a substantially larger river than currently flows there).Potholes State Park is a park on the shore of the Potholes Reservoir.It provides ready access to the Drumheller Channels National Natural Landmark which lies just downstream of the O'Sullivan Dam.