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National Geologic Map Database

Geologic Unit: Dean Lake

Usage:

No current usage.
(†Dean Lake Chert Member of Madison Limestone or †Dean Lake Chert (MT-local) considered abandoned.)


Geologic age:

Early Mississippian (Tournaisian; Kinderhookian)


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

Type locality: southeast side of Pentagon Mountain, in SW/4 sec. 14, T. 25 N., R. 14 W., [Pentagon Mountain 7.5-min quadrangle, Flathead Co.], northwestern MT. Named from Dean Lake, a small cirque lake lying at foot of cliffs that form upper part of east side of Pentagon Mountain (Deiss, 1933).


AAPG geologic province:

Montana folded belt
North Western Overthrust
Sweetgrass arch


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 ([ ]).