Erosion and uplifts formed the prairie landscape. Water, frost, and wind have cut gullies and gulches into the plains and sculpted benches or terraces along river valleys. Northeastern Montana prairie is broad, flat, and underlain by gravel beds. These high plains were formed 3–15 million years ago in a dry climate. The gravel layer allows efficient surface drainage, avoiding erosion and the channels and gullies of the badlands. Glacial debris has further enriched the soil, making this some of the state’s best agricultural land.
Montana’s badlands, desolate and vegetation-poor, tend to be found south of the Missouri, where glaciers did not deposit thick layers of good soil. Soft bedrock just beneath the surface of bare ground is easily eroded by rain; gullies form, with sediment outwashes spreading from their mouths. The bare, rain-pounded soil develops a hard crust, which exacerbates the runoff and makes it all the more difficult for any vegetation to take hold. The barrenness of the badlands perpetuates itself.