Initial Publication Date: June 17, 2005

Stratigraphy and Sedimentology of the Paleocene Fort Union Formation along the Powder River, Montana and Wyoming

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Start point

Broadus, MT

End point

near Arvada, WY

Roads (and Trails)

Powder River Road (between U.S. 212 in Broadus, MT and U.S. 14/16 (northeast of Arvada, WY)

Total distance

Not given.



The Paleocene Fort Union Formation in the Powder River Basin in Montana and Wyoming and adjoining areas contains a large number of very thick, closely spaced coal beds that make up some of the largest coal reserves in the United States. The main purpose of this field guide is to provide a knowledge of the stratigraphy, fluvial facies sequences, and depositional environments of portions of this coal resource at three main localities along the Powder River. Field data from measured sections and outcrop descriptions are synthesized into a depositional model for the origin of the Tongue River Member of the Powder River Formation.

Key Lithologic Features

  • Fort Union Formation (Tongue River Member): coal and carbonaceous shale (and associated clinker), sandstone, siltstone, shale, and limestone


  • sedimentary structures produced in ancient river channels and floodplains


  • Powder River Basin

Other Features

  • mollusc fossils


Flores, R.M., 1987, Stratigraphy and sedimentology of the Paleocene Fort Union Formation along the Powder River, Montana and Wyoming, in Beus, S.S., ed., Centennial Field Guide Volume 2: Rocky Mountain Section of the Geological Society of America , p. 19-88.


Out of print. Check Digital access to this publication is available via the links in the references section above.