Date of Award
Doctor of Philosophy (PhD)
McLean County, in west-central North Dakota on the east side of the Williston Basin, is covered by 8,500 to 13,000 feet of Paleozoic, Mesozoic, and Cenozoic rocks, which dip to the west at low angles. The Tertiary Tongue River and Sentinel Butte Formations are widely exposed in McLean County, and the Tertiary Cannonball Formation is exposed in a few places. Glacial drift, assigned to a new formation, the Coleharbor Formation, occurs throughout the county and reaches a maximum thickness of at least 400 feet in certain preglacial valleys.
The eastern part of McLean County, part of the Missouri Coteau, is dominated by hilly topography on dead ice moraine with associated lake sediments, ice-contact gravel deposits, and areas of collapsed outwash. Much of the remainder of the county is part of the Coteau Slope and is characterized by gently rolling topography on ground moraine. The Missouri Trench, with steep bedrock slopes, forms the western boundary of the county.
Glacial deposits of probable pre-Wisconsinan age were identified in McLean County, but little is known of either their exact age or the circumstances under which they were deposited. Glacial drift of probable Early Wisconsinan age covers most of the area of the Coteau Slope and Late Wisconsinan drift covers most of the Missouri Coteau. Both the Early and Late Wisconsinan glaciers stagnated as they thinned and receded from the area, resulting in hummocky areas of dead-ice moraine. The modern route of the Missouri River did not become firmly established until the Late Wisconsinan glacier receded from the area. This modern route of the river is a composite of several valley segments that range in age from preglacial to Late Wisconsinan.
Bluemle, John P., "Geology of McLean County, North Dakota" (1971). Theses and Dissertations. 28.