Geology

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Sedimentary rock formations in the Dakota Prairie Grasslands, like those found in the Badlands, developed over millions of years through the accumulation and consolidation of sediments, primarily sand, silt, and mud, deposited by wind, rivers, and ancient seas (Figure 1).

During the Mesozoic Era, shallow inland seas covered the region, and rivers flowing from the west deposited sediments. As the seas receded and rivers changed course, sand, silt, and mud (sediments) accumulated in the Dakota area. Over time, these sediments were compacted and cemented, forming sedimentary rocks such as sandstone and siltstone. Later, wind and water erosion sculpted the landscape into the distinctive badland terrain, with buttes, canyons, and valleys. 

Here are a few samples of sedimentary rocks found in the grasslands.

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The North Dakota Badlands are a distinctive, rugged landscape in the southwestern part of the state, characterized by steep slopes, deeply carved canyons, and unique geological formations such as buttes and spires.

This area results from extensive erosion of soft sedimentary rocks, particularly clays, by water and wind. Erosion is the dominant force shaping the landscape, carving the soft rocks into various forms.

The Little Missouri National Grassland's colorful, hilly landscape and beautiful badlands are prime examples of rugged terrain extensively eroded by wind and water, exuding a natural beauty at all times of day (Figure 2).

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Buttes (bee-yoots) are primarily located in western North Dakota, a common feature of the Badlands region in the Little Missouri National Grassland. Buttes are characterized by wind and water erosion. For example, White Butte (Figure 3) is the highest point in North Dakota (3,506 feet above sea level). The area contains various sedimentary rocks, including claystone, sandstone, and limestone. The white, bentonite-containing rocks and soil give it a unique appearance. Bentonite is a type of clay primarily made of montmorillonite, which can absorb and swell when wet. It forms from the decomposing volcanic ash. The buttes also contain fossil vertebrates, primarily mammals. White Butte is located in southwestern North Dakota, between Amidon and Bowman. It is a popular hiking destination for outdoor enthusiasts.

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The Burning Coal Vein area features a unique geological phenomenon: lignite coal (a low-grade, high-sulfur coal) has spontaneously ignited and burned over time. This results in a distinct badlands landscape with features and formations such as scoria (clinker) and bands of bright red and pink stony residue where the ground is heated and cracked.

While the underground fire is no longer active, the effects of past fires are still visible, particularly in the columnar juniper trees (Figure 4) and the landscape features. The burning coal vein is thought to have induced a unique columnar growth form in the area's Rocky Mountain juniper (cedar) trees.

The theory is that gases released by burning coal, particularly ethylene, influenced the tree's growth, causing it to develop a tall, narrow, columnar shape rather than its normal, more rounded form. Since the fire, the juniper trees have reportedly returned to their typical growth pattern.