Northern Prairie Wildlife Research Center
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
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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