Date of Award

1974

Document Type

Thesis

Degree Name

Bachelor of Science (BS)

Department

Geology

Abstract

The geology of 465 square kilometers adjacent to the confluence of the Yellowstone and Missouri Rivers in northwestern McKenzie County, North Dakota was mapped and the following interpretations were made. During late Pliocene or early Pleistocene time, the Yellowstone River deposited gravel (unit A) containing chert and volcanic and plutonic rocks; the upper surface of the gravel is about 90 meters above the present flood plains of the Yellowstone and Missouri Rivers. Subsequent downcutting was interrupted by a glacial advance that deposited sediment (unit B) across the entire area. The glacier dammed the Yellowstone River, forming a lake in which evenly bedded silt and clay (unit C) were deposited. As the glacier retreated, a series of outlet channels drained the lake. Yellowstone drainage was re-established and gravel (unit D) derived from local bedrock was deposited by tributaries of the Yellowstone River. Drainage was again disrupted by two additional glacial advances that deposited sediment (units E and F) over the entire area. As the last glacier retreated, gravel (unit G) containing chert and volcanic, plutonic, and carbonate rocks was deposited in a series of meltwater channels. The upper surface of this gravel is graded to about the level of the lowest terrace along the Yellowstone River. This terrace is underlain by grave l of unit G. Renewed downcutting established the present flood plains of the Yellowstone and Missouri Rivers and their tributaries.

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