Geologic units in Pennington county, Minnesota

Undifferentiated (Cenomanian to Campanian) at surface, covers 41 % of this area

Conglomerate, sandstone, mudstone, shale, marlstone, siltstone, and minor lignite, deposited in marine and non-marine settings; likely Cenomanian to Campanian age. Unit outline is the product of contouring the stratigraphic top and base, from which an isopach grid was created. Because the distribution is patchy, unit boundaries were drawn from the gridded data to represent locations where more than 25 feet (8 meters) of thickness occurs. As a result, many areas outside of the unit boundaries may be overlain by thin Cretaceous strata and the unit is depicted without a contact line.

Granodiorite to hornblende diorite, locally magmatically foliated (Neoarchean) at surface, covers 35 % of this area

Granodiorite to hornblende diorite, locally magmatically foliated. Includes the Britt Granodiorite (~2,685 Ma) and other intrusions having moderate gravity and magnetic signatures.

Mafic metavolcanic rocks (Neoarchean) at surface, covers 14 % of this area

Mafic metavolcanic rocks. Includes minor volcaniclastic and hypabyssal intrusive rocks metamorphosed to lower greenschist to lower amphibolite facies; includes the Ely Greenstone (~2,722 Ma).

Gabbro, peridotite, pyroxenite, lamprophyre, and metamorphic equivalents (Neoarchean) at surface, covers 5 % of this area

Gabbro, peridotite, pyroxenite, lamprophyre, and metamorphic equivalents. Includes the Oaks intrusion (~2,671 Ma) in the Wabigoon subprovince, and a ~2,639 Ma lamprophyre in the western Wawa subprovince; locally defined by variably high gravity and magnetic signatures.

Volcaniclastic rocks of felsic to intermediate composition (Neoarchean) at surface, covers 3 % of this area

Volcaniclastic rocks of felsic to intermediate composition.

Magnetic intrusions, undifferentiated (Archean) at surface, covers 1 % of this area

Magnetic intrusions, undifferentiated. Typically too small to ascertain gravity expression.

Granite to granodiorite (Neoarchean) at surface, covers 0.7 % of this area

Granite to granodiorite. Variably magnetic.

Biotite schist of graywacke protolith, and schist-rich migmatite (Neoarchean) at surface, covers 0.5 % of this area

Biotite schist of graywacke protolith, and schist-rich migmatite.