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An Environmental Overview of North Dakota: Past and Present

Geology and Soils

Next I would like to mention a little bit about geology and soils. The topography of North Dakota seems rather monotonous, but closer inspection reveals many complex and interesting geological features. The state traditionally has been divided by physiographers into two major areas, the Great Plains and the Central or Interior Lowlands. The dividing line between these two provinces is the western edge of the Missouri Coteau, a high hummocky area over which glacial stagnation occurred. Actually, all except the southwestern quarter and the eastern edge of the state is hummocky or rolling land dotted with thousands of small depressions of glacial origin. From east-to-west, the main topographic areas are the Red River Valley, Glacial Plains, Missouri Coteau, Missouri Plateau, and Badlands. The extremely flat Red River Valley occupies a strip along the eastern edge of the state. Geologically, this is not a river valley, but a remnant of the bottom of a giant glacial lake, Lake Agassiz. The valley contains North Dakota's most productive farmland. Between the Red River Valley and the Missouri Coteau are the glaciated plains or drift plains, a gently rolling area of ground moraine interrupted by several hummocky plateaus, numerous end moraines, and other glacial features such as outwash plains, lake plains, kames, and eskers. The Missouri Coteau consists primarily of dead ice moraine, with numerous areas of glacial outwash plain at lower elevations. To the west of the Missouri Coteau there is much less evidence of glaciation, even though the glaciers extended well into the present-day Missouri Plateau. Most of the landscape here has been shaped by running water and the grasslands have mostly developed over exposed bedrock, rather than glacial till. Especially rugged topography exists in the Badlands, a 2,000-square mile area of highly eroded bedrock that formed through glacial blockage of a major river.

Sedimentary deposits up to 16,000 feet thick cover the Precambrian Shield over all of North Dakota. Two kinds of sedimentary deposits are found in the state: bedrock and glacial sediment. Bedrock is found at or near the surface in most places southwest of the Missouri River, but is covered with various thicknesses of glacial sediment over most of the remainder of the state. Commonest bedrocks are marine shales and sandstones, and compacted continental silts, sands, clays, lignites, and limestones. Most of the glacial sediment is a loose mixture of pebbles, cobbles, sand, and silty clay termed glacial till. Also common are lake sediments of silt and clay and outwash areas and beach and shore deposits of loose sand and gravel. The great variety of sediment types causes complex groundwater patterns and great variation in the hydrological characteristics of soils and surface wetlands.

The surface of North Dakota slopes generally downward toward the northeast. Elevations range from 750 to 3500 feet above mean sea level. Most of eastern and northern North Dakota drains to Hudson Bay via the Red and Nelson rivers; the remainder drains to the Gulf of Mexico via the Missouri and Mississippi rivers.

Nearly all soils in North Dakota are frigid borolls with mean annual temperatures of less than 46°F. Predominant in the Interior Lowlands of eastern North Dakota are the highly fertile soils, characterized by a thick black layer of highly organic topsoil. In the Great Plains province, lighter soils predominate. These soils have a thinner, less fertile layer of topsoil that is brown in color, owing to a lesser amount of organic carbon. All these soils are used for cropland even though many have highly calcareous layers in the lower horizons due to leaching of minerals. Most of the remainder of North Dakota is overlain by soils that are highly calcareous throughout. These soils occur on steep slopes and are mostly used for pasture.

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