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Bayfield Co., Wisconsin, USA
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Bayfield County’s bedrock is dominated by a thick sequence of Precambrian rocks which occur in NE striking belts, with the oldest at the southern edge of the county. These oldest rocks in the section are poorly exposed Archean meta-volcanic and meta-sedimentary rocks. These are overlain by a thick section of Proterozoic sedimentary rocks, including the Bad River Dolomite,which was locally quarried as marble near Grandview. These are overlain by a thick section of 1.1 billion year old (Keweenawan) volcanic rocks. A few small native copper prospects occur in these rocks. These are intruded by the complexly differentiated Keweenawan–age plutons of the Mellen Complex. On top of these is a package of poorly-exposed Proterozoic sedimentary rocks (Oronto Group) which further filled the rift after the cessation of volcanism. The youngest bedrock, separated from the older rocks by another large thrust fault, the Douglas Fault, is the little metamorphosed Proterozoic Bayfield Group sandstones.The Bayfield Group is elegantly exposed on the Bayfield Peninsula, and the Apostle Islands. The Bayfield sandstones were formerly extensively quarried as building stone. The Apostle Islands are largely protected as a National Lakeshore. The islands are often fronted by wave-carved sandstone cliffs popular with tourists. They are most approachable in Big Bay State Park on Madeline Island.

Glacial drift and glacial lake sediments cover a lot of the county. The coarse tills and outwash can yield interesting minerals such as “drift” copper and Lake Superior agates.

The Northern Great Lakes Visitor Center located near Ashland near the junction of US highway 2 and Wisconsin Highway 13 is a great place to learn about this area's natural and human history.

Mineral List

Mineral list contains entries from the region specified including sub-localities
'Albite-Anorthite Series'
'Chlorite Group'
'K Feldspar'
var: Agate
var: Jasper
var: Lake Superior Agate

28 entries listed. 15 valid minerals.

Localities in this Region


The above list contains all mineral locality references listed on mindat.org. This does not claim to be a complete list. If you know of more minerals from this site, please register so you can add to our database. This locality information is for reference purposes only. You should never attempt to visit any sites listed in mindat.org without first ensuring that you have the permission of the land and/or mineral rights holders for access and that you are aware of all safety precautions necessary.


Cannon, W.F., L.G. Woodruff, S.W. Nicholson & C.A. Hedgman (1996) Bedrock geologic map of the Ashland and the northern part of the Ironwood 30' x 60' Quadrangles, Wisconsin and Michigan: U.S. Geological Survey, Miscellaneous Investigations Series: Map I-2566, 1 sheet.

Dott, R. H. Jr. & J.W. Attig (2004) Roadside Geology of Wisconsin, Mountain Press Publishing Company, 346 p.

Cannon, W. , G. LaBerge, J. Klasner & K. Schulz (2007) The Gogebic Iron Range - a sample of the northern margin of the Penokean fold and thrust belt: U. S. Geological Survey Professional Paper 1730, 44 p. plus map.

External Links

Wisconsin Mineral index - Wisconsin Geological and Natural History Survey http://wgnhs.uwex.edu/wisconsin-geology/minerals-wisconsin/

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Copyright © Jolyon Ralph and Ida Chau 1993-2014. Site Map. Locality, mineral & photograph data are the copyright of the individuals who submitted them. Site hosted & developed by Jolyon Ralph. Mindat.org is an online information resource dedicated to providing free mineralogical information to all. Mindat relies on the contributions of thousands of members and supporters. Mindat does not offer minerals for sale. If you would like to add information to improve the quality of our database, then click here to register.
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