Geologic units in Watonwan county, Minnesota

Middle and Upper Cambrian (Middle and Upper Cambrian) at surface, covers 34 % of this area

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

Undifferentiated (Cenomanian to Campanian) at surface, covers 25 % 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.

Upper Cambrian (Upper Cambrian) at surface, covers 23 % 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.

Sioux Quartzite (Paleoproterozoic) at surface, covers 12 % of this area

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).

Claystone, siltstone, and sandstone (Albian) at surface, covers 4 % of this area

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

Granitoid gneiss with dioritic to amphibolitic enclaves (Mesoarchean to Paleoarchean) at surface, covers 2 % of this area

Granitoid gneiss with dioritic to amphibolitic enclaves. Produces moderately high and varied gravity and magnetic signatures.

Granitic intrusion of unknown age (Archean or Paleoproterozoic) at surface, covers 0.1 % of this area

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