| Summary: | fusing together of the overlying shale and sand due to the heat of the burning lignite. The process is still going on today. In comparatively recent geological time, much of the northern and eastern parts of the state were covered by glacial ice, which was hundreds of feet thick. This ice brought rocks and other materials down from Canada and these were later transformed into fertile soil. The ice also blocked the northward-flowing Red River, forming the huge glacial Lake Agassiz, whose old bed now forms the fertile Red River Valley. The glaciers forced the old north-flowing rivers into their modem routes, and resulted in the formation of the modem Missouri River. Physiographic Regions in North Dakota North Dakota has a total area of 70,665 square miles. Of this, about 1,400 square miles, or just under two percent of the state's area, is water (this area changes somewhat as lakes expand and contract). The state is 310 miles wide at the Canadian boundary, 360 miles at the southern boundary. It is 210 miles from north to south. The state can be logically subdivided into several well-defined physiographic regions (fig. 1). These consist of separate areas of plains, which rise like steps from the east to the west. The easternmost plain is the old lake bed of glacial Lake Agassiz, the Red River Valley. This exceptionally flat plain is present on both sides of the river, and the North Dakota portion is from 30 to 40 miles wide. At the southern end, at Wahpeton, the elevation of the plain at the Red River is 965 feet, declining northward to an elevation of 750 feet at the Canadian border near Pembina (the lowest elevation in the state). Bordering the Red River Valley plain on the west is an escarpment, which is prominent in the northeastern part of the state, but much less so to the south. This escarpment, known as the Pembina or Manitoba escarpment, marks the eastern boundary of the Glaciated Plains, an area that is intermediate in elevation between the Red River plain on the east and the Missouri Plateau on the west. The area west of the escarpment is known as the Glaciated Plains because its surface is covered almost entirely by glacier deposits, to a considerable depth in places. However, glacier deposits are not limited to the Glaciated Plains, but are also found on the Missouri Plateau. Topographically, the Glaciated Plains consist of rolling land used mainly for farming. A number of lakes, the largest of which is Devils Lake, are also found here. On the west, rising above the Glaciated Plains, is the 300 to 400-foot-high Missouri Escarpment, which marks the eastern boundary of the Missouri Coteau. The Missouri Coteau consists of rugged glacial topography. It is considered to be part of the Central Lowland. The western edge of the Missouri Coteau coincides with the eastern edge of the Great Plains, a broad, relatively flat area of rolling 510 Chapter 12 Physical Characteristics and Resources of North Dakota
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