It's a strange and seemingly complicated place. From the ragged ridges and saw-toothed spires to the wind-ravaged desolation of Badlands Wilderness Area, Badlands National Park is an awe-inspiring sight and an unsettling experience. Few leave here unaffected by the vastness of this geologic anomaly, which spreads across 381 square miles of moonscape.
The Lakota Indians who once traversed this incredible land named it mako sica, or "land bad." Early French-Canadian trappers labeled it les mauvaises terres à traverser, or "bad lands to travel across."
Steep canyons, towering spires, and flat-topped tables all appear among Badlands buttes. Despite their apparent complexity, the unusual formations of the Badlands are essentially the result of two basic geologic processes: deposition and erosion.
The layered look of the Badlands comes from sedimentary rocks composed of fine grains that have been cemented into a solid form. Layers with similar characteristics are grouped into units called formations. The bottom formation is the Pierre Shale, deposited 68 to 77 million years ago during the Cretaceous period, when a shallow, inland sea stretched across the Great Plains. The mud of the sea floor hardened into shale, leaving fossil clamshells and ammonites that confirm a sea environment. The sea eventually drained away, and the upper layers of shale were weathered into soil, now seen as Yellow Mounds.
The Chadron Formation, deposited 34 million to 37 million years ago during the Eocene epoch, sits above the Pierre Shale. By this time, a flood plain had replaced the sea, and each time the rivers flooded, they deposited a new layer of sediment on the plain. Alligator fossils indicate that a lush, subtropical forest covered the region. However, mammal fossils dominate. The Chadron is best known for large, elephant-size mammals called titanotheres.
Some of the sediment carried by rivers and wind was volcanic ash, the product of eruptions associated with the creation of the Rocky Mountains. This ash mixed with river and stream sediments to form clay stone, the main material from which Badlands buttes are constructed. After the Eocene epoch, the climate began to dry and cool, and tropical forests gave way to open savanna. Rivers deposited the Brule and Sharps formations during the Oligocene epoch from 28 to 34 million years ago, and today these formations contain the most rugged peaks and canyons of the Badlands.
Actually, the impressive serrated ridges and deep canyons of the Badlands did not exist until about 500,000 years ago, when water began to cut through the layers of rock, carving fantastic shapes into what had been a flat flood plain. Once again, the ancient fossil soils, buried for millions of years, became exposed. That erosion continues: Every time rain falls, or snow melts in spring, more sediment is washed from the buttes in this ongoing work of sculpting the earth. On average, the buttes erode an inch a year; scientists believe that the buttes will be gone in another 500,000 years.
In addition to its scenic wonders, the Badlands are one of the richest Oligocene fossil beds known to exist. Remains of three-toed horses, dog-size camels, saber-toothed cats, giant pigs, and other species have been found here; all date from 28 million to 37 million years ago.