The Great Plains were blanketed with a fall of volcanic ash nearly 12 million years ago. This unique park contains the fossil skeletons of animals that died at a watering hole following that massive volcanic eruption. The fossil bed has been uncovered and left in place for public viewing. The Rhino Barn covers the excavation area. Declared a National Natural Landmark. Visitor center, exhibits and trails. Open Memorial Day Weekend-Labor Day, Mon-Sat, 9am-5pm; Sun, 11am-5pm. Limited hours in May, Sep & Oct. Special arrangements can be made for tour or school groups. Park permit required. Admission: $7 ages 3 and up.