Rain and melting snow, wind, frost, and other forces of erosion have carved our badlands into intricate shapes. Since the Little Missouri River began to form the badlands, it has removed an enormous amount of sediment from the area. In the southern part of the badlands, near the river’s headwaters and close to Devils Tower in northeastern Wyoming and adjacent Montana, the river has cut down about 80 feet below the level at which it had been flowing before it was diverted by a glacier farther north. Near Medora, the valley floor is 250 feet lower than the pre-diversion level. Still farther downstream, in the North Unit of Theodore Roosevelt National Park and near the confluence of the Missouri and Little Missouri rivers, and nearer to where the glacier diverted it, the east-trending portion of the Little Missouri River flows at a level that is 650 feet deeper than when it was diverted.
The average rates of erosion in the badlands, assuming they started to form about 640,000 years ago, can be calculated as follows:
Headwaters area in Wyoming: 0.15-inch/100 years;
Medora area: 0.5-inch/100 years;
Confluence area near Mandaree – Missouri and Little Missouri rivers: 1.25 inch/100 years.
These rates may seem tiny but, over time, erosion has removed a huge amount of sediment. Approximately 40 cubic miles of sediment have been eroded and carried away by the Little Missouri River from the area that is now the badlands. Most of that sediment now lies beneath the water of the Gulf of Mexico.
The rates of erosion I’ve noted are long-term averages, but erosion goes on at highly irregular rates. Locally, considering only the past few hundred years, the badlands have undergone four separate periods of erosion and three periods of deposition. Since about 1936, new gullies have been cut to their present depths. It may seem a paradox that, although running water is the main agent of erosion, badlands formation tends to be most intense when water is in short supply. Why? Because erosion tends to be more vigorous during times of drought when the vegetative cover is too sparse to protect the soil from the occasional rain storm or spring snow melt. When precipitation is sufficient for the growth of heavy vegetation, the soil is better protected from severe erosion.
Streams and rivers carry sediment away from the area of the badlands, but most of the actual “on-the-spot” erosion is a result of slopewash. In places where vegetation is sparse, the soil and rock materials are easily weathered, forming loose surfaces that slide downslope easily, slumping and sliding during showers or when the snow cover melts.
The Badlands Landscape
The shapes, sizes, and configurations of the hills, buttes, valleys, and other landforms in the badlands are not entirely happenstance. Differences in hardness of the materials result in differences in resistance to erosion. Nodules and concretions help to shape a landscape ranging from beautiful, to desolate – even grotesque. Hard beds of sandstone or clinker cap many of the small buttes. Variations in permeability (permeability is a measure of the ease with which water can move through porous rock) have similar effects; rain and melted snow soak into the more open and permeable sands, resulting in only minimal erosion. When water flows over the surface of tighter, less permeable sediment, such as clay, it abrades and erodes the material, carrying some of it away. The presence or absence and the character of the vegetation also play important roles in governing the rate of erosion. Grass usually helps to control erosion more effectively than does forest vegetation.
The irregular placement of hard nodules and concretions may result in the development of rock-capped pillars, known as “hoodoos,” mushroom-like shapes perched on stalks of clay. In places, slopes are covered by nodules of siderite (iron carbonate). As they weather out of the surrounding materials, becoming concentrated on the surface, the copper-colored nodules form an erosion-resistant armor, which temporarily slows the rate of erosion. Clinker beds are also much more resistant to erosion than are the softer surrounding beds. We commonly see buttes capped by red clinker beds.
Erosional “pipes” sometimes form in gullies and ravines where surface runoff is focused. “Piping” results where runoff can flow downward into small cracks and joints. Pipes are common in places where surface runoff erodes cavities vertically downward through the soft rock. With time, the initial pathways may widen at depth into caves the size of small rooms. The average depth of vertical pipes is about 10 to 15 feet, but some are much deeper. The tops of pipes may be partially concealed making hiking treacherous. I have seen the bones of animals, such as rabbits and deer, at the bottoms of pipes (so far I haven’t seen any human bones). The animals fell into the holes and could not get out.
The geology is only part of the badlands story. The weather and climate, vegetation, animals, birds, insects, sounds and aromas–all of these, along with the human history and the ranching heritage, work together to complete the story of the badlands.
I think the North Dakota badlands are particularly beautiful because of their parklands; wooded areas that occur in draws and on north-facing slopes. Heavy vegetation in the badlands in places like Little Missouri State Park adds to the scenery. Evergreens, such as the Rocky Mountain juniper, ponderosa, and creeping juniper are interspersed with quaking aspen, cottonwood, and poplar. Limber pines are found in the badlands in the southwest corner of the state, near Marmarth.
I’ve hiked and camped in the badlands many times. Evening summer showers accentuate the colors and the clinker beds assume intense shades of red and orange. The fresh, pungent aroma of wet sage and cedar enhance the experience. At night, the stark, intricately eroded pinnacles can seem unreal. In the moonlight or in a night lightning storm, it is easy to imagine the strange shapes as ruins of a magical city, rather than structures of mere sand and clay. Blend in the sound of coyotes conversing and the badlands environment is complete.
As you travel through western North Dakota, notice the multicolored layers and brick- or glass-like masses of baked and fused clay, shale, and sandstone. These baked materials, known as clinker, but often referred to locally as “scoria,” formed in areas where seams of lignite coal burned, baking the nearby sediments to a natural brick. Clinker beds range in thickness from a few feet to more than 50 feet in North Dakota, with even thicker beds in Wyoming and Montana.
The first recorded reference to clinker that I know of was by William Clark, who made the following entry in his journal while wintering at Fort Mandan (March 21, 1805):
Saw an emence quantity of Pumice Stone on the sides & feet of the hills and emence beds of Pumice Stone near the Tops of them, with evident marks of the hills having once been on fire. I Collecte Somne of the different sorts i.e. Stone Pumice & a hard earth, and put them into a funace, the hard earth melted and glazed the others two and the hard Clay became a pumice Stone glazed.
When Lewis and Clark arrived at Beulah Bay, about 20 miles west of present-day Riverdale, on April 10, 1805, Lewis noticed a seam of lignite burning along the face of an outcrop. He commented:
“the bluff is now on fire and throws out considerable quantities of smoke which has a strong sulphurious smell.”
On April 16, 1805, Meriwether Lewis wrote the following:
I believe it to be the strata of coal seen in those hills which causes the fire and birnt appearances frequently met with in this quarter. where those birnt appearances are to be seen in the face of the river bluffs, the coal is seldom seen, and when you meet with it in the neaghbourhood of the stratas of birnt earth, the coal appears to be presisely at the same hight, and is nearly of the same thickness, togeter with the sand and a sulphurious substance which usually accompanys it.
Following Lewis and Clark, numerous explorers mentioned seeing clinker as they traveled through the region. They included Larocque (1805), Maximilian (1833), Nicollet and Fremont (1839), and Audubon (1843). Some of these explorers believed the clinker beds had a volcanic origin, but Lewis and Clark were correct in their appraisal that clinker formed as clay and sand were heated by the underlying lignite when it caught fire due to natural causes, such as lightning or prairie fires.
Several early explorers reported seeing coal fires in the northern Great Plains. Over the years, range fires have ignited lignite beds many times. At Buck Hill, in the South Unit of Theodore Roosevelt National Park, a lignite seam burned from 1951 until 1977. During early October, 1976, prairie fires burned over large areas in the southwestern part of the state, igniting underground lignite seams in at least 30 locations over a 7,000-acre area near Amidon. Most of the fires were extinguished before the following spring, but some of them burned for several months. Again, in July, 1988, several lignite seams were ignited by widespread fires in the badlands. Juniper tree roots burning downward from the surface, into the coal, ignited some of the fires.
Burning lignite is limited to depths where adequate air circulates from the surface. The level of the water table may control this depth (burning can’t take place in water-saturated materials). While veins of coal are burning, fumes from the smoldering coal can alter the growth habits of nearby vegetation, causing it to grow in unusual shapes. After the fires go out, the vegetation reverts to its normal shape, common elsewhere in the badlands. Near Amidon, a stand of junipers grew as columnar-shaped trees for many years while a nearby lignite seam burned, producing ethylene gas, which altered the growth habit of the trees. Since the fire went out, the trees have resumed their normal, more bush-like shapes.
Heat from burning lignite beds hardens, melts, or sinters the overlying and surrounding rocks into brick or glass. Sintering is a process that fuses material into a hard mass, without melting it, much like bricks are baked in a kiln. When lignite burns, it may be transformed to an ash bed that takes up only a fraction of the space the lignite did before it burned. Thin layers of white ash, mostly potash, lime, and other inorganic, non-combustible minerals, can sometimes be found at the base of clinker beds.
The baking process oxidizes iron-rich minerals, mainly to red shades, but black, gray, purple, yellow, and other hues are common. The hue and intensity of the colors depends upon the mineral composition, the grain size of the material that was baked, and how hot a temperature was reached during the baking process. The brick-red color, which is most common, is due primarily to the presence of the mineral hematite (iron oxide: the same as common rust). Following a rain shower, wet clinker beds are much brighter in color.
By the time the materials overlying a burning lignite bed cool and collapse, they are hard, and usually partially fused by baking. As they slump, falling into the burned-out space, the baked, melted, and sintered materials may hold together, resulting in a mass that can be as much as 75 percent air space. After the clinker cools, the empty spaces provide convenient living places for small animals, such as rattlesnakes.
Several prominent clinker zones are found throughout the Little Missouri Badlands. The clinker forms a cap on many hills and ridges over extensive areas. Clinker resists erosion because it is harder than unbaked rocks and also because heating and subsidence during the baking process produce fractures that allow water to infiltrate, minimizing surface runoff. Erosion often leaves clinker as a cap on red-topped knobs, ridges, and buttes standing above the more subdued nearby topography developed on less-resistant, unbaked materials. Some widespread areas of clinker are particularly scenic; good examples can be seen along the Red Hills Road south of Sentinel Butte, along the Bennie Pier road in McKenzie County, and on parts of the Scenic Loop Drive in the South Unit of Theodore Roosevelt National Park.