Usage:
Mason Group (IL*)
Subunits:
(alphabetical) --all in IL*: Equality Formation, Henry Formation, Peoria Silt, Roxana Silt.
Geologic age:
Pleistocene (Wisconsinan Age); uppermost part considered Holocene*
Type section, locality, area and/or origin of name:
Type locality: Mason Co., central IL. Named from Mason Co. (Hansel and Johnson, 1996).
Principal reference sections (Hansel and Johnson, 1996):
(1) Farm Creek section, on south side of Farm Creek, in NE/4 SW/4 SE/4 sec. 30, T. 26 N., R. 3 W., Washington 7.5-min quadrangle, Tazewell Co., IL
(2) Wedron section, in highwalls of pits in Wedron Silica Company quarries, in secs. 8, 9, 10, and 16, T. 34 N., R. 4 E., Wedron 7.5-min quadrangle, La Salle Co., IL.
AAPG geologic province:
Illinois basin*
Michigan basin*
Wisconsin 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 conflicts with nomenclatural guidelines (CSN, 1933; ACSN, 1961, 1970; NACSN, 1983, 2005, 2021). May be explained within brackets ([ ]).