Geologic units in Mahnomen county, Minnesota

Granitic intrusion (Neoarchean) at surface, covers 52 % of this area

Granitic intrusion. Includes the Sacred Heart (~2592, 2,603 Ma) and Ortonville granites, the Shannon Lake Granite (~2,674), and other intrusions having low gravity and magnetic signatures.

Mafic metavolcanic rocks (Neoarchean) at surface, covers 26 % 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).

Granite to granodiorite (Neoarchean) at surface, covers 15 % of this area

Granite to granodiorite. Variably magnetic.

Granitoid intrusion (Neoarchean) at surface, covers 5 % of this area

Granitoid intrusion. Constrained solely by low gravity and magnetic signatures.

Calc-alkalic volcanic and volcaniclastic rocks (Neoarchean) at surface, covers 3 % of this area

Calc-alkalic volcanic and volcaniclastic rocks.