Geologic units in Sherburne county, Minnesota

Middle and Upper Cambrian (Middle and Upper Cambrian) at surface, covers 55 % of this area

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

Gray granodiorite to granite intrusions (Paleoproterozoic) at surface, covers 13 % 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.

Granite (Paleoproterozoic) at surface, covers 10 % 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.

Granitic to granodioritic orthogneiss (Neoarchean) at surface, covers 9 % of this area

Granitic to granodioritic orthogneiss. Includes the McGrath Gneiss (~2,752 ± 15, 2,557 Ma) and unnamed units.

Mille Lacs and North Range Groups and equivalent sedimentary rocks (Paleoproterozoic) at surface, covers 4 % of this area

Includes the Mahnomen and Rabbit Lake Formations and Trout Lake marble. Unit descriptions from GEOLEX - Mahnomen Formation: Upper member described as gray to light-gray siltstone, argillite, and fine-grained quartzose sandstone containing irregularly distributed beds and lenses of iron-formation and allied anomalously iron-rich sedimentary rocks; base of unit defined arbitrarily as the top of the lowermost mappable iron-formation layer of the middle, iron-formation member. Middle, iron-formation member--interlayered cherty and slaty iron-formation that is similar lithologically to the smaller iron-formation lenses within the upper and lower members; contains rocks formerly assigned to the Trommald Formation and the Emily Member of the Rabbit Lake Formation (Morey, 1978). Lower member--predominantly siltstone, fine- to medium-grained quartzose graywacke, and argillite; also includes minor quartz arenite and irregularly distributed layers and lenses of anomalously iron-rich sedimentary rocks. Rabbit Lake Formaiton: gray to very dark-gray slate, siltstone, and very fine-grained graywacke; includes irregularly distributed layers and lenses of carbonaceous slate and also carbonate- and sulfide-facies iron-formation, chiefly in the lower part of the unit.

Interlayered volcanic, volcaniclastic, sedimentary, and hypabyssal intrusive rocks (Paleoproterozoic) at surface, covers 4 % 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 rocks, undifferentiated (Paleoproterozoic) at surface, covers 2 % of this area

Granitic rocks, undifferentiated. Largely inferred from geophysical maps.

Granitoid intrusions, variably magnetic (Paleoproterozoic) at surface, covers 1 % of this area

Granitoid intrusions, variably magnetic. Includes the Ann Lake granite (~1,784 Ma) and Glendorado pluton (~1,788 Ma).

Upper Cambrian (Upper Cambrian) at surface, covers 1 % 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.

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).

Sandstone, siltstone, and local conglomerate (Mesoproterozoic) at surface, covers 0.3 % 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.

Gabbro, pyroxenite, diorite, and lamprophyre (Paleoproterozoic) at surface, covers 0.2 % 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).

Undifferentiated (Cenomanian to Campanian) at surface, covers < 0.1 % 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.