Geologic units in McLeod county, Minnesota

Claystone, siltstone, and sandstone (Albian) at surface, covers 25 % of this area

Claystone, siltstone, and sandstone. Albian age is tentatively inferred from a single analysis of pollen.

Foliated to gneissic tonalite, granodiorite, and diorite (Neoarchean) at surface, covers 20 % of this area

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.

Leucogranite (Neoarchean) at surface, covers 10 % of this area

Leucogranite. Occurs along the Yellow Medicine Shear Zone and elsewhere, primarily in batholithic settings.

Little Falls Formation (Paleoproterozoic) at surface, covers 9 % of this area

Schist and slate of graywacke-mudstone protolith.

Granite (Paleoproterozoic) at surface, covers 7 % of this area

Granite, reddish, variably porphyritic, massive; includes the St. Cloud Red (~1,779 Ma), Foley (~1,774, 1,779 Ma), Pierz (~1,779 Ma), and Pease granites, and Richmond charnockitic granite (~1,772 Ma). An unnamed granite in south-central Minnesota is slightly older at ~1,792 Ma.

Interlayered volcanic, volcaniclastic, sedimentary, and hypabyssal intrusive rocks (Paleoproterozoic) at surface, covers 6 % of this area

Interlayered volcanic, volcaniclastic, sedimentary, and hypabyssal intrusive rocks. Includes parts of the Mille Lacs Group, North and South Range Groups, and Glen Township Formation.

Granitic orthogneiss and migmatite (Mesoarchean to Paleoarchean) at surface, covers 5 % of this area

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

Sandstone, siltstone, and local conglomerate (Mesoproterozoic) at surface, covers 5 % of this area

Sandstone, siltstone, and local conglomerate. Includes the Hinckley Sandstone and Fond du Lac (youngest detrital zircons ~1,000 Ma) and Solar Church Formations; deposition in eolian, fluvial, and lacustrine environments.

Gray granodiorite to granite intrusions (Paleoproterozoic) at surface, covers 4 % of this area

Gray granodiorite to granite intrusions. Includes the Reformatory (~1,783 Ma), Freedhem (~1,775, 1,776 Ma), Isle (~1,779 Ma), and Warman (~1,787 Ma) intrusions.

Granitic intrusion of unknown age (Archean or Paleoproterozoic) at surface, covers 3 % of this area

Granitic intrusion of unknown age. Low gravity and magnetic expression.

Middle and Upper Cambrian (Middle and Upper Cambrian) at surface, covers 3 % of this area

Sandstone, siltstone, and shale; includes the Wonewoc Sandstone, Eau Claire Formation, and Mt. Simon Sandstone.

Upper Cambrian (Upper Cambrian) at surface, covers 2 % of this area

Sandstone, siltstone, shale, and dolostone; includes the Jordan Sandstone and St. Lawrence Formation, and the Mazomanie, Lone Rock, and Davis Formations of the Tunnel City Group.

Granitoid gneiss with dioritic to amphibolitic enclaves (Mesoarchean to Paleoarchean) at surface, covers 1.0 % 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 0.8 % 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.

Mafic intrusions including pyroxenite, peridotite, gabbro, and lamprophyre (Paleoproterozoic) at surface, covers 0.6 % 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).

Gabbroic to dioritic intrusion (Archean or Paleoproterozoic) at surface, covers 0.3 % of this area

Gabbroic to dioritic intrusion. High to moderate gravity and magnetic signature. Includes Providence and Cottonwood intrusions in southwestern Minnesota.

Gabbro, pyroxenite, diorite, and lamprophyre (Paleoproterozoic) at surface, covers < 0.1 % of this area

Gabbro, pyroxenite, diorite, and lamprophyre. Includes the Watab quartz diorite (~1,780 Ma), St. Wendell quartz gabbro, and an unnamed diorite (~1,786 Ma).