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.
Granitic orthogneiss and migmatite. Geophysical map patterns imply this unit intruded other gneisses.
Mafic volcanic and hypabyssal intrusive rocks of uncertain age. Adjacent to and within the Yellow Medicine shear zone.
Quartzite, mudstone, and local conglomerate of fluvial and marine origin (~1,760 to 1,630 Ma; 1,902 ± 55 Ma rhyolite pebble in basal conglomerate).
Gabbroic to dioritic intrusion. High to moderate gravity and magnetic signature. Includes Providence and Cottonwood intrusions in southwestern Minnesota.
Granitoid gneiss with dioritic to amphibolitic enclaves. Produces moderately high and varied gravity and magnetic signatures.