In the Oglala National Grassland north of Crawford, a pocket of badlands has worn into clay pedestals topped with slabs of harder sandstone, the toadstools of the name. The softer silts and clays under the caps erode faster than the caps themselves, and many of the big ones have already fallen. The grassland is named for the Oglala Lakota.
The rock is the White River Group, laid down roughly 45 to 24 million years ago by streams that wandered across a flat savanna carrying sediment from the rising Rockies. Its lower part, the Chadron Formation, takes its name from the town to the east. The layers are full of the animals of that world: brontotheres standing eight feet at the shoulder, the entelodont Archaeotherium, herds of oreodonts, the early horse Mesohippus, early camels and rhinoceroses, saber-toothed cats and tortoises up to three feet across. Some of them left tracks in falls of volcanic ash, and the tortoise trails still show the line of a dragging tail. Collecting is against federal law.
A one-mile interpretive loop runs through the formations from the campground, and the Bison Trail leaves it for three miles to the Hudson-Meng center, built over a bone bed of Bison antiquus about 10,000 years old. Near the trailhead the Forest Service built a sod house in 1984 beside the site of a 1929 homestead soddy. The last nearly 13 miles in are gravel, and the Forest Service warns against them when wet.
The closest stops worth working into your route
Roadside plaques and monuments within a short detour