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National Geologic Map Database

NGMDB

Geologic Unit: Montana

Usage:

Montana Group (KS,MT*,ND,SD)


Subunits:

(alphabetical): Bearpaw Shale (MT*), Big Skunk Formation (MT), Claggett Formation (MT*,WY*) or Claggett Shale (MT*,WY*), Eagle Formation (ND) or Eagle Sandstone (MT*), Fox Hills Formation (ND,MT*), Gammon Shale (MT*), Golden Spike Formation (MT*), Hell Creek Formation (MT), Horsethief Sandstone (MT*), Judith River Formation (MT*), Lennep Sandstone (MT*), Parkman Sandstone (MT*), Pierre Shale (ND,SD,MT*), Telegraph Creek Formation (MT*), Two Medicine Formation (MT*), Virgelle Sandstone (MT*).


Geologic age:

Late Cretaceous (Santonian to Maastrichtian)*


Type section, locality, area and/or origin of name:

Named from extensive development in Montana, especially in Upper Missouri River region (US geologic names lexicons, USGS Bull. 896, 1200).


AAPG geologic province:

Montana folded belt*
Central Montana uplift*
Sweetgrass arch*
Powder River basin*
Williston basin*
Green River basin*


NGMDB

For more information, please contact Nancy Stamm, Geologic Names Committee Secretary.

Asterisk (*) indicates usage by the U.S. Geological Survey. Other usages by state geological surveys.

"No current usage" (†) implies that a name has been abandoned or has fallen into disuse. Former usage and, if known, replacement name given in parentheses ( ).

Slash (/) indicates name does not conform with nomenclatural guidelines (CSN, 1933; ACSN, 1961, 1970; NACSN, 1983, 2005). This may be explained within brackets ([ ]).

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Page Last Modified: Thu Sep 14 19:43:37 2017