Geology of Badlands National Park

December 01, 2021

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Photographers: Charlene Lanik Sauls, Brian Sauls

Summary Author: Brian Sauls

The geology comprising the Badlands National Park in southwestern South Dakota is a colorful layer-cake of various sedimentary rocks deposited between 28 to 75 million years ago by shallow seas, rivers, and wind. The distinct rock layers consist of multi-colored sandstone, siltstone, mudstone, claystone, limestone, shale, and volcanic ash. Remarkably, the volcanic ash originated from volcanoes located over 500 miles (800 km) away in present day Nevada and Utah, which was blown eastward before settling in the park area. Over time, this deposited ash hardened into beige-colored volcanic tuff through the process of lithification.

In addition to geologic deposition, the Badlands Park region was further shaped by tectonic forces approximately 5 million years ago. The tectonics primarily shifted the underlaying rock strata through uplifting and folding forces. Since this period of the geologic history, the Badlands has been continually shaped by erosion as it has gradually formed the hills, valleys, stream channels, and other interesting features of this park. Because the rock layers are relatively soft, erosion occurs at a high rate of about one inch per year. At this rapid rate of erosion, estimates suggest that the hills of the Badlands will erode completely within the next half a million years. Photos taken in August 2021.

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