A Sod Story: Ancient Prairies of the Badlands

an elevated patch of prairie with steep walls stands above green grasslands.
Sod tables in Badlands National Park represent an ancient prairie.

NPS Photo

an elevated portion of prairie stands over green grasses and in front of badlands canyons.
Sod tables can be seen throughout the park.

NPS Photo

Setting the Table

Throughout the Badlands are broken sections of grass and soil that sit on top of badlands material, like in the picture below. These features are known as sod tables, for the sod (or soil) that covers them and their flat, table-like tops. The soil and grass of sod tables protect the rock below from erosion by soaking up rain during intense storms, while the exposed rock around sod tables cannot absorb water and quickly washes away. The different rates of erosion make it appear like sod tables are springing up out of the Badlands, when they are really wearing away more slowly than the rock around them.

roots grow into the exposed soil of a sod table with grasses stretching skyward.
Sod tables are a great place to get a view of prairie grass root systems.

NPS Photo

Ancient prairies

Sod tables are the last traces of ancient prairies. At the end of the last ice age, the Badlands had a cooler and wetter climate. At that time, many sections of the park that today are exposed rock would have been covered by extensive prairies. As the environment slowly warmed and dried, erosion (caused by storms and flowing rivers) began to cut channels into these prairies. Once the protective layer of sod was removed, the rock beneath began quickly eroding away. In this way, the broad grasslands of the past became the isolated sod tables of today.

twelve small (around 1 inch in length) worked stones sit on a green fabric with a scale bar.
Many archaeological finds have been made on the surface of sod tables.

NPS Photo

Treasure Troves

Most of the archaeological sites found in Badlands National Park have been discovered in sod tables, such as those surrounding the Ancient Hunters Overlook. Tools, pottery, charcoal fragments, and butchered bison bones from ancient inhabitants of the Badlands are preserved in the sod -- some up to 12,000 years old! These sites are invaluable clues for understanding the history of human habitation in the Badlands, and become exposed as erosion wears away the edges of sod tables.

badlands canyons descend into green grasses and sod tables.
As the Badlands erode away, new sod tables will form.

NPS Photo

Future Tables

Along many sections of the Badlands Loop Road, an unbroken prairie stretches away to the north of the Badlands Wall. As erosion continues to strip away the rocks of the Badlands, that prairie is likely to become dissected and fragmented, with small pockets of remaining grasslands standing above the eroded badlands below -- new sod tables! From the Pinnacles overlook, the spectacular view of canyons and sod tables to the south is a vision of what the grassland to the north will become.

Part of a series of articles titled Badlands Geology and Paleontology.

Badlands National Park

Last updated: November 10, 2020