| Summary: | ash) sandstones. About 5 million years ago, long after the lakes were filled, a new erosional cycle began. The relatively hard ruffs and freshwater limestones and sandstones 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 and carried away by streams and rivers to Hudson Bay. The Killdeer Mountains, with their resistant caprock, are the result of that erosion cycle; they are the modern manifestation of an ancient lake bed. Two sites in the Killdeer Mountains are of particular interest. The Killdeer Battle State Historic Site is located on the southeast edge of the area (Section 34, T146N, R96W). The "Battle of the Killdeer Mountains" took place on July 28, 1864, when General Sully and 3,000 troops used artillery on 6,000 Teton and Yanktonai Sioux in revenge for the uprising of Santee Sioux in southern Minnesota. Sully defeated the Sioux, killing many of them and destroying their camp and equipment. At the top of the southeast spur of the Killdeer Mountains is Medicine Hole, a "cave" about 10 feet across and 90 feet deep. This was the traditional location for the place where, according to Native Americans living there, all animals and people came out of the earth at the beginning of time. Medicine Hole is located on the Medicine Hole Plateau, in the south half of Section 22 and the north half of Section 27, T146N, R96W. In this one-square-mile area, the Arikaree Formation is especially well exposed. The Killdeer Mountains support the largest deciduous forest in southwestern North Dakota, except for the forests of the floodplains bordering the major rivers. The Killdeer 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 typically found in more boreal settings, 200 miles or more to the northeast. Although the Killdeer Mountains were apparently not covered by the continental glaciers, their topography dates largely to the Pleistocene. Remnants of old stream-cut surfaces � pediments � flank the Killdeers. These pediments, which cut across all of the older formations, are capped by about 10 feet of sand and gravel. Old ice wedges can be seen in the gravel in places, testimony to the time when the area was subjected to tundra conditions during one or more of the glacial epochs. In summary, the Killdeer Mountains are an erosional outlier, preserved because of their resistant caprock of tufaceous sandstone and limestone. Erosion of the area that began in late Pliocene and continued into early Pleistocene time resulted in gravel-covered surfaces (pediments) around the flanks of the Killdeer Mountains. These gravel deposits, which were derived from the sandstone and limestone beds higher up in the Killdeers, are themselves resistant to further erosion and they help to retard the ongoing, modern erosion cycle. The present erosion cycle began when the nearby Little Missouri River was diverted from its northerly route by a glacier so that it flowed instead to the 538 2001-2003 North Dakota Blue Book
|
|---|