Several years ago, billboards were posted around North Dakota in an effort to entertain and catch motorists’ attention. One of them, outside of Mandan, read “North Dakota Mountain Removal Project Completed.” The billboard referred to the image many people have of North Dakota as a flat and featureless land, but the sign ignored the fact that, within our borders are at least half-a-dozen features bearing the name “mountain.” Was the removal project a failure?
One of our mountainous areas is the Killdeer Mountains in western North Dakota, about 40 miles due north of Dickinson. Another is Turtle Mountain, home of the International Peace Garden on the North Dakota-Manitoba border. (Turtle Mountain is singular, not plural; I’ll explain later). It may seem odd that the Killdeer Mountains, Turtle Mountain, and several other features in North Dakota are called “mountains.” The idea may be related somewhat to scale. When viewed by a person who has recently traveled over eastern North Dakota, the features may be impressive, but I wonder what they might have been named if more of our settlers had come via Wyoming or Montana.
We have several more places in North Dakota that bear the name “mountain.” The town of Mountain in Pembina County was settled by Icelanders in 1873. Mountain is situated on the former shoreline of glacial Lake Agassiz, and the view from there, over the Red River Valley, is impressive. Just north of Mountain, the hilly area along the Pembina River Valley in northeastern North Dakota is sometimes referred to as “Pembina Mountain,” but the term “Pembina Hills” is commonly used as well. The steep escarpment is also referred to as the “Pembina Escarpment” or “Manitoba Escarpment.” Pioneer geologist David Dale Owen, when he traveled through the Red River Valley in 1848, commented on Pembina Mountain thus: it is “in fact no mountain at all, nor yet a hill. It is the terrace of table land – the ancient shore of a great body of water that once filled the Red River Valley.” People have been critical of the kind of mountains we have in North Dakota ever since! (Owen was from Indiana).
Other named “mountains” in North Dakota include Devils Lake Mountain in southeastern Ramsey County, Blue Mountain in western Nelson county, Lookout Mountain in northeastern Eddy County, and the Prophets Mountains in western Sheridan County. All of these features are ice-thrust hills or complexes of ice-thrust topography that stand as high as a few hundred feet above the surrounding areas. Near Medora, in Billings County, we have Tracy Mountain, but we don’t have many “mountains” in southwestern North Dakota – in that area the term “butte” is used more often. Several hundred formally named features called “hills” or “buttes” are found in North Dakota, as well as a few “points” and “ridges.” Many of these are at least as impressive as some of our mountains. We also have many features that fit the formal definition of a mesa, but very few of them have been referred to as mesas. I won’t dwell any longer on the vagaries of naming topographic features. The names don’t necessarily make much sense. We do manage to communicate, at least if we stay close to home. This article will deal mainly with the Killdeer Mountains and I will follow it with an article on Turtle Mountain. Both features are of considerable scenic beauty no matter what you want to call them and both have interesting stories to tell. The Killdeer Mountains
The Killdeer Mountains consist of two large, flat-topped buttes in Dunn County. They cover an area of 115 square miles and rise from 700 to 1,000 feet above the surrounding plains. The entire elevated Killdeer Mountain region is about nine miles long and six miles wide. The highest elevation in the area is 3,314 feet, which is 192 feet lower than the highest point in the state (White Butte). The term “Killdeer” is presumably a translation of a Sioux phrase: “Tah-kah-p-kuty” (the place where they kill the deer).
The caprock on the Killdeer Mountains consists of a 300-foot-thick sequence of siltstone, sandstone and carbonate beds that belong to the Miocene-age Arikaree Formation. One of the most conspicuous, ledge-forming units within the Arikaree Formation is found about 150 feet below the caprock. Known as the “burrowed marker unit” or “wormy marker bed,” it is a sequence of hard, erosion-resistant interbedded siltstone and sandstone with some carbonate lenses (the burrows in the bed were dug by clams living in the sediment before it hardened; the organisms that did the digging were similar to modern “shipworms”). The Arikaree Formation lies on top of the Eocene-age Chadron Formation, a sequence of yellow to green sandy mudstone, clayey sandstone, and pebbly sandstone. The tree-covered, slopes around the flanks of the Killdeer Mountains are mainly landslide topography, consisting of materials that have fallen or slid from higher up. A little farther away, the grassy or farmed, less-hilly areas are underlain mostly by the Golden Valley Formation, a Paleocene to Eocene-age rock unit. The Paleocene Sentinel Butte Formation, which underlies the Golden Valley Formation beneath the Killdeer Mountains, occurs at the surface in a broad area surrounding the Killdeer Mountain upland.
The two main buttes that make up the Killdeer Mountains coincide with areas that were once lakes in which sandy and limy sediments, along with some stream deposits, accumulated during Miocene time. Repeated volcanic eruptions in the Rocky Mountains to the west produced large amounts of ash, which blew eastward, fell to the ground, and washed into the lakes, forming tuffaceous (meaning they contain volcanic ash) sandstones.
A new erosion cycle began about five million years ago, long after the lakes had filled with sediment, and dried up. The relatively hard tuffs and freshwater limestone and sandstone beds that had been deposited in the Miocene lakes were much more resistant to erosion than were the surrounding sediments. Because of their resistance to erosion, these hard materials remained standing above the surrounding area as the softer Golden Valley and Sentinel Butte sediments were eroded away by streams and rivers. The Killdeer Mountains, with their resistant caprock, are the result of that erosion; they are the modern manifestation of ancient lake beds. The topography has undergone a complete reversal; areas that were once low are now high due to their resistance to erosion.
Two sites in the Killdeer Mountains are of particular interest. The Killdeer Mountain Battle State Historic Site is located on the southeast edge of the Killdeer Mountains, seven miles northwest of the town of Killdeer (Section 34, T. 146 N., R. 96 W.). The Battle of the Killdeer Mountains took place on July 28, 1864 when General Sully and 2,200 troops used artillery on 6,000 Teton and Yanktonai Sioux in revenge for the uprising of Santee Sioux in southern Minnesota. Sully decimated the Sioux, killing many of them and destroying their camp and equipment. Less than a year earlier, on September 3, 1863, Sully had accomplished a similar feat at the Battle of Whitestone Hill, where his troops killed, captured or wounded 300 to 400 Sioux Indians. Medicine Hole is, indeed, a hole in the ground, but it is not a cave in the traditional sense because it did not form as most caves do. No solution of carbonates was involved, and there are no stalactites or stalagmites. It is, rather, a crack in the ground, where a large block of material has begun to fall away from the main body of the southern butte of the Killdeer Mountain. Medicine Hole is located on private land and, as I write this, in 2015, the area is not open to public access. Please respect the wishes of the land owner. The Killdeer Mountains support the largest deciduous forest in southwestern North Dakota, except for the forests on the floodplains bordering the major rivers. The Killdeer Mountain forest consists largely of aspen and oak, with some ash, elm, birch, and juniper, along with shrubs such as chokecherry, willow, plum and buffaloberry. The forest is interesting in that it contains species that tend to be found in more boreal settings, areas that may be 200 miles or more to the northeast.
In summary, the Killdeer Mountains are an erosional feature, preserved because of their resistant caprock of tuffaceous sandstone and limestone. Erosion of the area began in late Miocene time, and continued into Pleistocene time, resulting in gravel-covered, flat, sloping surfaces (pediments) around the flanks of the Killdeer Mountain uplands. These gravel deposits, up to ten feet thick, were derived from the sandstone and limestone beds higher up in the Killdeers. The gravels are themselves resistant to further erosion and they help to retard the rate of the ongoing, modern erosion cycle. The current erosion cycle began when the nearby Little Missouri River was diverted by a glacier from its northerly route so that it flowed (flows) eastward to its modern confluence with the Missouri River. As a result of the diversion, and the resulting steeper gradient over which it flows, the Little Missouri River began to erode vigorously, carving the badlands through which the modern river flows today. Although the Killdeer Mountains show no evidence of ever having been glaciated, their modern topography dates largely to the Pleistocene. Old ice wedges can be seen in the pediment gravels in places, testimony to the time when the area was subjected to tundra conditions during one or more of the glacial epochs. There were no glaciers over the Killdeers, but continuous frigid conditions provided a tundra ecosystem. *Frost Wedges: Frost wedges are common, but many areas of patterned ground that have been interpreted to be frost polygons are really dessication cracks developed in silcrete. These are much older than frost wedges, such as this one, which formed in loose materials.