The Book Cliffs Range stretches from Western Colorado along the Grand Valley deep into Utah to the west. Composed mostly of Mancos Shale badlands along its flanks, this section of the cliffs is capped by Mesa Verde Sandstone. This top layer of sandstone protects the softer shale below from quickly eroding away. The Mancos Shale is the ancient seabed from the Cretaceous Interior Seaway that bisected North America about 80 million years ago before this region was uplifted as part of the Colorado Plateau. Photo © copyright by Chris Eaton.