They are thought to have been very agressive, perhaps fighting among themselves. Here and there in the Oligocene Badlands, conditions were right for the fossilization of plant roots. The roots and other evidence prove that the Badlands formations consist mostly of fossil soils, one stacking atop the other as one layer of mud after another was deposited and converted into soil, only to be covered with fresh mud by the next flood. One scientist counted 87 fossil soils from the earliest of the Badlands formations to the most recent. The rain-eroded buttes may look desolate, but they are not.
Every rain frees from their flanks fossil plants and animals of an ancient landscape.
In the late 1950's, park planners struggled with the problem of how to exhibit the park's fossils in the field. It seemed obvious how to do it. Find an area rich in fossils, remove enough of the Badlands rock so that visitors could clearly see the fossils, and build a trail connecting the specimens. But it was not that easy. Even at the most promising site, the site of the present trail, the variety and quality of fossils accessible to a trail simply were not there.