Geologic units in Chippewa county, Wisconsin

Cambrian, undivided (Cambrian) at surface, covers 71 % of this area

Sandstone with some dolomite and shale, undivided; includes Trempealeau, Tunnel City, and Elk Mound Formations

Gneiss, migmatite, and amphibolite (Late Archean) at surface, covers 24 % of this area

Quartzofeldspathic gneiss and less abundant amphibolite and migmatite. Includes granitoid rocks. Granitic gneiss at Port Edwards, WI on Wisconsin River has a U-Pb zircon age of 2870 +/- 13 Ma, and gneiss at Jim Falls in Chippewa River valley has a U-Pb zircon age of 2522 +/- 22 Ma (Sims and others, 1989)

Felsic volcanic and volcanogenic rocks (Early Proterozoic) at surface, covers 3 % of this area

Tuff, argillite, graywacke, and minor volcanic rocks of lower greenschist-facies in southern Rusk County. Could be younger in age than adjacent metavolcanic rocks.

Granitic rocks, undivided (Early Proterozoic) at surface, covers 1 % of this area

Gray, weakly foliated to massive granite in poorly exposed areas.

Mafic to felsic metavolcanic rocks (Early Proterozoic) at surface, covers 0.6 % of this area

Volcanic rocks in areas of sparse geologic data and nondefinitive magnetic and gravity data

Quartzite (Early Proterozoic) at surface, covers 0.5 % of this area

Maroon but locally white, gray, and red quartzite (quartz arenite) with a basal quartzose conglomerate. At Flambeau Ridge (Chippewa County) consists of conglomerate. Distinguished from other quartzite units in being strongly deformed and metamorphosed. Includes Flambeau, Rib Mountain, McCaslin, and Thunder Mountain Quartzites of local usage

Granite-tonalite (Early Proterozoic) at surface, covers 0.1 % of this area

Gray to pinkish-gray, medium-grained, generally equigranular granite to tonalite and granitoid gneiss; locally includes diorite. Intrudes older metavolcanic rocks. Zircon ages range from 1852 +/- 15 to 1862 +/- 5 Ma