 The glaciated plains are generally covered in clay, gravel, sand, and silt left by the proglacial Lake Great Falls or by moraines or gravel-covered former lake basins left by the Wisconsin glaciation 85,000 to 11,000 years ago.Farther east, areas such as Makoshika State Park near Glendive and Medicine Rocks State Park near Ekalaka contain some of the most scenic badlands regions in the state.The Hell Creek Formation in Northeast Montana is a major source of dinosaur fossils.