Located in southwest South Dakota is the beautiful and fascinating terrain of Badlands National Park. This park encompasses 381 square miles (987 square km) of colorful, jagged hills that decorate one of the largest remaining mixed-grass prairies in the United States.
Situated in this park are ancient sediments spanning tens of millions of years. These rocks and soils contain a myriad of fossils from the organisms that lived in the varied ecosystems that once existed here. The prairie that exists today nurtures a number of equally impressive animals, including bison and pronghorn.
The sediments that make up these gorgeous hills were deposited from about 75 to about 28 million years ago. During the late Cretaceous Period when dinosaurs still ruled the earth, the Great Plains were inundated by a vast inland sea. The mud that accumulated in that sea was later buried by younger sediment and turned to stone, preserved today as the Pierre Shale. As the tectonic collision and uplift of the Laramide Orogeny formed the Rocky Mountains and Black Hills to the west, this area too began to see higher and drier times. As the top layers of shale were exposed to the air they slowly weathered into the contrasting Yellow Mounds.
Between about 37 and 34 million years ago this area was blanketed by a vast floodplain. Runoff from the new, higher elevations to the west created numerous streams and rivers that flowed through this region. The rounded, gray hills of the Chadron Formation contain alligator fossils, supporting other evidence that this location was once closer to the equator and more tropical at that time. From then on tectonic activity would slowly move North America away from the equator.
The alternating tan and red layers of the Brule Formation were deposited from about 34 to 30 million years ago. This formation contains interbedded mudstones, siltstones, sandstones, and ash from volcanoes to the west.
From about 30 to 28 million years ago North America continued to gradually migrate to the north and west, away from the equator. As the North American plate overrode the Pacific and Juan de Fuca Plates, subduction generated significant volcanism to the west of the Badlands. Volcanic ash is a significant component of the Rockyford Ash and Sharps Formation, and today they represent the most jagged peaks in the park.
Sediment accumulation likely continued here for millions of years as streams and rivers carried weathered particles from the Black Hills and deposited them in this area. That all changed about half a million years ago when the Cheyenne River captured these streams and changed their course. Waterways no longer deposited sediment here and instead began to carry it away. Erosion began in earnest, leading to the landscape that exists today.
Erosion acts relatively quickly on the soft rocks of the Badlands, and it’s estimated that they will be completely gone within the next few hundred thousand years. As the hills erode, however, they expose a library of animal fossils from the last few tens of millions of years. Although fossils can be found throughout the park, they’re front and center on display along the Fossil Exhibit Trail.
Fossil casts of many large, impressive prehistoric animals are on display here, along with interpretive signs. Some of the more interesting include rhino-like mammals known as titanotheres…
…as well as the saber-toothed cat-like mammals known as nimravids:
Today equally impressive mammals still roam these hills, including herds of American bison (Artiodactyla: Bovidae: Bison bison)…
…pronghorn (Artiodactyla: Antilocapridae: Antilocapra americana)…
…black-tailed prairie dogs (Rodentia: Sciuridae: Cynomys ludovicianus)…
…as well as rabbits:
Along the stream beds one can even find amphibians seeking solace in the few moist places among the Badlands:
Grasses and wildflowers also blanket the prairies here, including sunflowers…
…and snow on the mountain:
Badlands National Park is equal parts geologic history and prairie ecology. One can travel back through the last few tens of millions of years of earth history here along the roadways, marvel at the beautiful rocks that were formed in the varied environments, and be delightfully interrupted along the way by the impressive organisms that live here today.
Most people seem to visit the eastern reaches of this park, sticking to the comfortable lodge, developed campground, and paved roads found here. Although I only spent two days in this park, it seemed as if the real treasures were to be found to the west. Along the remote gravel roads are more animals, more plants, and a deeper understanding of the geologic history. Near the western extent of the park is the Sage Creek Campground, a pleasantly primitive area free from traffic and crowds. It was amazing to fall asleep under the dark sky and abundant stars while listening to the howls of coyotes.