Geologic units in Oconto county, Wisconsin

Prairie du Chien Group (Ordovician) at surface, covers 19 % of this area

Dolomite with some sandstone and shale; includes Shakopee and Oneota Formations

Wolf River batholith; Hager Formation; Rhyolite member (Middle Proterozoic) at surface, covers 19 % of this area

Gray to reddish-gray, slightly foliated, porphyritic rhyolite containing aligned phenocrysts of alkali feldspar and lesser amounts of plagioclase in a fine-grained matrix of feldspar, biotite, amphibole, and sparse quartz

Sinnipee Group (Ordovician) at surface, covers 16 % of this area

Dolomite with some limestone and shale; includes Galena, Decorah, and Platteville Formations

Cambrian, undivided (Cambrian) at surface, covers 14 % of this area

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

Wolf River batholith; Wolf River Granite (Middle Proterozoic) at surface, covers 8 % of this area

Red, coarse-grained rapakivi granite consisting of large (1-3 cm) ovoid alkali feldspar sporadically mantled by plagioclase, interstitial plagioclase, quartz, biotite, hornblende, and ilmenite

Mafic to felsic metavolcanic rocks (Early Proterozoic) at surface, covers 8 % of this area

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

Wolf River Batholith; Belongia Granite (Middle Proterozoic) at surface, covers 6 % of this area

Red to pink granite consisting of both a coarse-grained and a fine-grained facies. Probably an epizonal intrusion

Ancell Group (Ordovician) at surface, covers 4 % of this area

Orthoquartzitic sandstone with minor limestone, shale and conglomerate; includes Glenwood and St. Peter Formations

Bimodal mafic and felsic metavolcanic rocks (Early Proterozoic) at surface, covers 4 % of this area

High-aluminum basalt to low-silica andesite pillowed flows and interlayered dacite to rhyolite tuffs and porphyries in Monico and Mountain areas, northeastern Wisconsin. A rhyolite porphyry at Jennings (Oneida County) has an age of 1869 +/- 6 Ma. Rocks are host to massive sulfide deposits (Crandon and Pelican River)

Quartzite (Early Proterozoic) at surface, covers 0.9 % 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

Wolf River batholith; Red River Granite (Middle Proterozoic) at surface, covers 0.7 % of this area

Contains alkali feldspar phenocrysts (0.5-2 cm), subordinate plagioclase and quartz, and rare clusters of biotite with or without hornblende

Wolf River batholith; Hager Formation; Quartz porphyry member (Middle Proterozoic) at surface, covers 0.7 % of this area

Contains 30-45 percent resorbed quartz phenocrysts (3-4 mm) and less abundant alkali feldspar and plagioclase phenocrysts (4-5 mm) in a fine-grained matrix of quartz, two feldspars, biotite, and hornblende

Peshtigo Mangerite in the Wolf River batholith; Peshtigo Mangerite (Middle Proterozoic) at surface, covers 0.4 % of this area

Brown to dark-gray, coarse-grained (0.3-1.5 cm) inequigranular monzonite containing subhedral, zoned plagioclase, alkali feldspar, mafic silicates (fayalite, hypersthene, ferroaugite-hedenbergite, hornblende, and biotite), and interstitial quartz

Wolf River batholith; High Falls Granite (Middle Proterozoic) at surface, covers 0.4 % of this area

Gray to pink, equigranular to porphyritic granite to granodiorite containing microcline microperthite, concentrically zoned plagioclase, quartz, biotite, and hornblende