Geologic units in Stevens county, Minnesota

Granitic orthogneiss and migmatite (Mesoarchean to Paleoarchean) at surface, covers 39 % of this area

Granitic orthogneiss and migmatite. Geophysical map patterns imply this unit intruded other gneisses.

Schist and tonalitic to granodioritic paragneiss (Neoarchean) at surface, covers 25 % of this area

Schist and tonalitic to granodioritic paragneiss. Typically adjacent to large batholithic complexes.

Granitic intrusion (Neoarchean) at surface, covers 10 % 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.

Schist of sedimentary protolith (Neoarchean) at surface, covers 7 % of this area

Schist of sedimentary protolith. Metamorphosed to upper greenschist to amphibolite facies.

Granitoid gneiss with dioritic to amphibolitic enclaves (Mesoarchean to Paleoarchean) at surface, covers 6 % of this area

Granitoid gneiss with dioritic to amphibolitic enclaves. Produces moderately high and varied gravity and magnetic signatures.

Undifferentiated (Cenomanian to Campanian) at surface, covers 6 % 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.

Granitoid intrusion (Neoarchean) at surface, covers 4 % of this area

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

Volcaniclastic rocks of felsic to intermediate composition (Neoarchean) at surface, covers 2 % of this area

Volcaniclastic rocks of felsic to intermediate composition.

Foliated to gneissic tonalite and granodiorite (Mesoarchean to Paleoarchean) at surface, covers 1 % of this area

Foliated to gneissic tonalite and granodiorite.

Mafic intrusions including pyroxenite, peridotite, gabbro, and lamprophyre (Paleoproterozoic) at surface, covers 0.3 % of this area

Mafic intrusions including pyroxenite, peridotite, gabbro, and lamprophyre. Defined largely by magnetic signature. One intrusion in Morrison County is ~1,791 Ma, and lithologically similar intrusions cut the Foley Granite (~1,774 Ma).