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America's Volcanic Past

"Though few people in the United States may actually experience an erupting volcano, the evidence for earlier volcanism is preserved in many rocks of North America. Features seen in volcanic rocks only hours old are also present in ancient volcanic rocks, both at the surface and buried beneath younger deposits." -- Excerpt from: Brantley, 1994

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Map, Location of Wisconsin

Volcanic Highlights and Features:
[NOTE: This list is just a sample of various Wisconsin features or events and is by no means inclusive. All information presented here was gathered from other online websites and each excerpt is attributed back to the original source. Please use those sources in referencing any information on this webpage, and please visit those websites for more information on the Geology of Wisconsin.]

  • Wisconsin
  • Wisconsin Regions
  • Wisconsin - Brief Geologic History
  • Rib Hill


Although many people know that glaciers once covered much of the State, few realize that there were once volcanoes, lofty mountains, and tropical coral reefs in Wisconsin at various times in the distant past.

Excerpt from: The Weis Earth Science Museum Website, University of Wisconsin, 2002

Wisconsin Regions

Superior Upland Province:1
Every continent has a core of very ancient metamorphic rocks. The Superior Upland Province is the southern extension of the Laurentian Upland Province, part of the nucleus of North America called Canadian Shield . The basement rocks of the Laurentian Upland Province were metamorphosed about 2,500 million years ago in a mountain-building collision of tectonic plates called the Kenoran orogeny. The rocks of the Superior Upland are mostly Precambrian metamorphic rocks and overlying Paleozoic rocks (Cambrian) covered by a thin veneer of glacial deposits left behind when glaciers melted at the end of the Pleistocene Ice Age. If we could strip away all of the younger rocks deposited on top of buried Precambrian basement, you would see a landscape of low relief. The topography of the Precambrian rocks is very subdued, with barely 500 feet difference between the highest point and the lowest. Clearly, this region was exposed to a very long period of erosion in the very distant past which beveled the original mountainous surface to a gently undulating surface. The present surface is not much different. Hills rise just a few hundred feet above the surrounding countryside. The highest of these, such as Rib Hill, Wisconsin, are made up mostly of resistant quartzite or granite.

The Interior Plains:1
The Interior Plains is a vast region that spreads across the stable core (craton) of North America. This area had formed when several small continents collided and welded together well over a billion years ago, during the Precambrian. Precambrian metamorphic and igneous rocks now form the basement of the Interior Plains and make up the stable nucleus of North America. With the exception of the Black Hills of South Dakota, the entire region has low relief, reflecting more than 500 million years of relative tectonic stability.

Wisconsin - Brief Geologic History

Argillite, Amphibolite, Anorthosite, Basaltic to rhyolitic lava flows, Gabbro, Basaltic to rhyolitic metavolcanic rocks with some metasedimentary rocks, Diorite, Gneiss, Granite, Graywacke, Meta-gabbro and hornblende diorite, Metavolcanic rocks, Quartzite, Sandstone, Siltstone, Syenite

Sandstone with some dolomite and shale

Dolomite, Dolomite with sandstone and shale, Dolomite with some limestone and shale, Sandstone with some limestone shale and conglomerate, Shale


Dolomite and shale


Rib Hill

Rib Hill:1
Made up mostly of resistant quartzite or granite.

Excerpts from:
1) USGS/NPS Geology of the Parks Website, 2001
2) Wisconsin Geological and Natural History Survey Website, 2002, Bedrock Geology of Wisconsin Map (1981, revised 1995)

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01/28/03, Lyn Topinka