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National Geologic Map Database

Geologic Unit: Marias River

Usage:

Marias River Shale of Colorado Group (MT*)


Subunits:

(alphabetical) --all in MT: Cone Member*, Ferdig Member*, Floweree Member*, Holter Sandstone Member, Kevin Member*.


Geologic age:

Late Cretaceous (Cenomanian to Santonian)*


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

Named from excellent exposures along the Marias River, which flows eastward across Sweetgrass arch between South arch and Kevin-Sunburst dome, between T. 30 and 31 N., R. 4 E. to 5 W., Liberty and Toole Cos., MT. Here, most of formation is exposed in Marias River saddle, along boundary between Liberty and Toole Cos. Forms bedrock on most of Sweetgrass arch and extends westward into Rocky Mountains (Cobban and others, 1959).


AAPG geologic province:

Montana folded belt*
Sweetgrass arch*


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

Asterisk (*) indicates published by U.S. Geological Survey authors.

"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 ([ ]).