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| | North Dakota |
 | | The sandstone is stained yellow by limonite toward the base, where it unconformably overlies the clay and silty claystone of the Amidon member. |
 | | Geologists speculate that an ancestral Yellowstone River deposited these alluvial materials when it flowed south-southeast through Slope County, in a deep valley it had eroded into the older units below, much as the modern Missouri River is cutting into older rocks today north of Bismarck. |
 | | Hoganson, John W., 1986, Oligocene stratigraphy of North Dakota in Clausen, Eric and Allen J. Kihm, Tertiary and upper Cretaceous of south-central and western North Dakota: North Dakota Geological Society, 1986 Field Trip, p.36-40. |
| www.unh.edu /esci/north_dakota.html (342 words) |
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