|Name||Grand River Formation|
Sedimentary > Clastic > Sandstone (Bed)
Sedimentary > Clastic > Mudstone > Shale (Bed)
|Comments||Secondary unit description from USGS Geologic Names lexicon (ref. MI016): Named the Grand River group in MI for the Grand River where it flows from Jackson Co. to Ionia Co. Pennsylvanian formations which are stratigraphically above the Saginaw group have been variously called Woodville, Ionia, and Red beds. However, either term, Woodville or Ionia, implies correlation of all younger beds than the Saginaw although there are few facts to substantiate such correlation. The Grand River group includes various formations, which stratigraphic evidence indicates are younger than the Saginaw, though not strictly to be correlated with each other as occupying the same position in the geologic time scale. Group includes the Woodville sandstone, Ionia sandstone, Eaton sandstone, and any other formations correlated with them. The Grand River is of Pennsylvanian age.|
Milstein, Randall L. (compiler), 1987, Bedrock geology of southern Michigan: Geological Survey Division, Michigan Dept. of Natural Resources, scale 1:500,000.
USGS Geologic Names lexicon found at: http://ngmdb.usgs.gov/Geolex/
|Counties||Clinton - Eaton - Gratiot - Ingham - Ionia - Shiawassee|