The White River Bad Lands is the most important Bad Land area in the World. Nowhere in the world can the influence of erosion be better studied or more easily understood. This area lies chiefly in southwestern South Dakota. No place shows better how the Lord built up the rocks and soils of the land. Layers of muds, sands and gravels were laid down through unnumbered years and were accompanied by animals that were suited to the weather and geography of the time. This is the reason that fossils of different animals are found at different layers of depth in the Bad Lands.