Usage:
Alaska Bench Limestone of Amsden Group (MT*,ND*)
Alaska Bench Limestone Member of Amsden Formation (MT,ND)
Geologic age:
Early to Middle Pennsylvanian (Morrowan to Atokan)*
Type section, locality, area and/or origin of name:
[Named from Alaska Bench, notably in T. 13 N., R. 20 E., Alaska Bench 7.5-min quadrangle, Fergus Co., central MT.] Forms series of hogbacks and sloping benches around Big Snowy Mountains (Freeman, 1922; GNC index card files).
Reference section (Amsden Group): Stonehouse Canyon, from center of west line sec. 25, T. 11 N., R. 20 E., eastward into SW/4 SW/4 sec. 29, T. 11 N., R. 21 E., thence down dry canyon southward across N/2 NW/4 sec. 31, T. 11 N., R. 21 E., [Sahara Hill and Patterson Canyon 7.5-min quadrangles], Golden Valley Co., central MT (Maughan and Roberts, 1967; see also Gardner, 1959).
AAPG geologic province:
Central Montana uplift*
Montana folded belt*
Powder River basin*
Sweetgrass arch*
Williston basin*
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 conflicts with nomenclatural guidelines (CSN, 1933; ACSN, 1961, 1970; NACSN, 1983, 2005, 2021). May be explained within brackets ([ ]).