Geology
Learning about the science behind the beauty greatly enhances your enjoyment and appreciation of Badlands National Park.
The bizarre landforms called badlands are, despite the uninviting name, a masterpiece of water and wind sculpture. They are near deserts of a special kind, where rain is infrequent, the bare rocks are poorly consolidated and relatively uniform in their resistance to erosion, and runoff water washes away large amounts of sediment. On average, the White River Badlands of South Dakota erode one inch per year. Erosion is so rapid that the landforms can change perceptibly overnight as a result of a single thunderstorm.
It is an account of 75 million years of accumulation with intermittent periods of erosion that began when the Rocky Mountains reared up in the West and spread sediments over vast expanses of the plains. The sand, silt, and clay, mixed and interbedded with volcanic ash, stacked up, layer upon flat-lying layer, until the pile was thousands of feet deep. In a final phase of volcanism as the uplift ended, white ash rained from the sky to frost the cake, completing the building stage.
During the Oligocene epoch 40 to 25 million years ago, the region that is now the White River Badlands supported many kinds of animals. The land was then lush, well watered, and much warmer than now. The animals, mostly mammals, roamed the floodplains; many died in floods and were quickly buried in river sediments. Conditions for preservation were excellent; the Oligocene beds are one of the world's richest vertebrate fossil sites.
Broad regional uplift raised the land about 5 million years ago and initiated the erosion that created the Badlands. The White River, which now flows west to east five or ten miles south of the park, eroded a scarp, the beginning of what is now called the Wall.
Numerous small streams and rills furrowed the scarp face and eventually intersected to create the Badlands topography. Each rainstorm over the next 5 million years chewed away at the Wall, making its crest recede northward away from the river as its base followed suit.
The physical character of the Badlands varies considerably according to the nature of the materials. For example, the frosting of volcanic ash at Badlands National Park succumbs quickly as the Wall advances northward into the upper plain—the original land surface—exposing the more durable underlying beds of the Brule formation. Nature's answer to great resistance is to carve steeper slopes, resulting here in incredibly slender spires above knife-sharp ridges and intricately creased slopes. Deeper into the layer cake, the more rounded ridges and spurs, and gentler slopes, reflect the softer mudstone of the Chadron formation. Numerous "islands" of Chadron mudstone dot the plain in front of the Wall. They are remnants, soon to be gone, of the earlier, ever changing Badlands.
* Information provided by the Park Service
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