Granitic orthogneiss and migmatite. Geophysical map patterns imply this unit intruded other gneisses.
Leucogranite. Occurs along the Yellow Medicine Shear Zone and elsewhere, primarily in batholithic settings.
Granitoid gneiss with dioritic to amphibolitic enclaves. Produces moderately high and varied gravity and magnetic signatures.
Foliated to gneissic tonalite, granodiorite, and diorite. Includes the Lookout Mountain tonalite (~2,718 Ma) of the Giants Range batholith and other intrusions within batholithic complexes defined by a low-to-moderate gravity signature with magnetic foliation apparent from aeromagnetic maps.
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.
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 and slate of graywacke-mudstone protolith.
Gabbroic to dioritic intrusion. High to moderate gravity and magnetic signature. Includes Providence and Cottonwood intrusions in southwestern Minnesota.
Granite to granodiorite. Variably magnetic.
Mylonitic, gneissic, and schistose rocks of plutonic and volcanic protolith.
Mafic volcanic and hypabyssal intrusive rocks of uncertain age. Adjacent to and within the Yellow Medicine shear zone.
Gabbro, pyroxenite, diorite, and lamprophyre. Includes the Watab quartz diorite (~1,780 Ma), St. Wendell quartz gabbro, and an unnamed diorite (~1,786 Ma).
Granodiorite to hornblende diorite, locally magmatically foliated. Includes the Britt Granodiorite (~2,685 Ma) and other intrusions having moderate gravity and magnetic signatures.
Mylonite, varied protolith. Age of shearing unknown and likely protracted.
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).