Portage County Bedrock from the Bedrock Geology of Portage County

Bedrock Geology of Portage County, Wisconsin Map ¹⁵

^{This map is a more detailed look at the
bedrock geology of the County, than the clipping from the state of Wisconsin
bedrock map.}

Color	Symbol	Rock Type	Description	Period	Era	Eon
	ss	Sandstone Undifferentiated	well to poorly sorted quartz arenites, commonly iron-oxide cemented, feldspathic, and conglomeratic near the Cambrian/Precambrian unconformity. Red and green shales occur locally.	Cambrian	Paleozoic	Phanerozoic
	ai	Anorgenic Intrusive Rock of the Wolf River Batholith (1500 million years ago)	coarse to medium grained ademellite (quartz monzonite).	Middle Proterozoic	Proterozoic	Precambrian
	qmr	Quartzite and Associated Metasedimentary Rocks	orthoquartzite, pink to green, white, gray or yellowish; conglomerate with quartz and rock claste; argillite, micaceous quartzited, chert; iron formation and iron-rich quartzite/chert	Early Proterozoic	Proterozoic	Precambrian
	ag	Anorogenic Granite	pink to red biotite-granite, typically granophyic; also two-mica equigranular granite.	Early Proterozoic	Proterozoic	Precambrian
	kg	Syn-to Late-Kinematic Granitic Rocks	red to pink biotite-granite, and granodiorite, typically equigranular massive to porphyritic; granitic rocks	Early Proterozoic	Proterozoic	Precambrian
	mi	Mafic Intrusive Rock	gabbro and pyroxenite, underformed to well-foliated	Early Proterozoic	Proterozoic	Precambrian
	pkgt	Pre-to Syn-Kinematic Intermediate Intrusive Rocks, and Tonalites along the Wisconsin River (1840 million year ago)	grandiorite to tonalite, coarse-grained equigranular to porphyritic with abundant biotite and hornblende, typically well-foliated; tonalites gray to white, coarse to fine-grained with well-developed foliation and lineation, intruded by granitic dikes	Early Proterozoic	Proterozoic	Precambrian
	ih	Intrusive Hybrids	granite/felsic-intermediate volcanic hybird, fine-grained gray to gneissic-banded gray to pink rock, also biotite schist; granite/mafic volcanic hybrid, pin/black "salt and pepper"-textured rock or mafic banded-gneiss, also hornblende schist.	Early Proterozoic	Proterozoic	Precambrian
	vr	Felsic to Intermediate Volcanic Rocks-originally pyroclastic and porphyritic rocks	quartz-sericite schist/phyllite and biotite-chlorite schist; quartzofeldspathic gneiss, some with feldspar porphyroblasts; pink to gray granitic felsites and prophyries, mostly fine grained.	Early Proterozoic or Early Archean	Proterozoic or Archean	Precambrian
	mur	Mafic Volcanic Rocks-originally flows, volcaniclastic and diabase rocks	chlorite, actinolite, and hornblende schist with amphibolite at higher metamorphic grade, rare preservation of amygdaloidal and pillow structures	Early Proterozoic or Early Archean	Proterozoic or Archean	Precambrian
	gn	Gneiss Along the Wisconsin River (2800 million years ago)	quartzofeldspathic gneiss and migmatite, well-layered/banded, granite to tonalite in composition, with amphibolite and biotite schist subordinate. Intruded by Proterozoic tonalite and several generations of granite pegmatites.	Late Archean	Archean	Precambrian

To view the Portage County clipping from the Bedrock Geologic Map of Wisconsin, click here.

(Source: Greenberg and Brown ¹⁴⁾