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.
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.
Amphibolitic to dioritic gneiss.
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.
Granitic orthogneiss and migmatite. Geophysical map patterns imply this unit intruded other gneisses.
Granite to granodiorite. Variably magnetic.
Granitic intrusion of unknown age. Low gravity and magnetic expression.
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).
Gabbroic to dioritic intrusion. High to moderate gravity and magnetic signature. Includes Providence and Cottonwood intrusions in southwestern Minnesota.