Penokee Iron Range Trail: Plummer Mine Geologic Layer Cake

Photographed June 19, 2015
Montreal, Iron County, Wisconsin
Google Map

Between 1 to 1 1/2 million years ago sediments of slate and cherty iron carbonates were laid down on top of the granite and greenstone bedrock covering this area. Molten lava flowed over the land, seeping into the great cracks on the surface creating “dikes.” Then the land was submerged under a great glacial sea and more layers, of sandstone and conglomerate rock, were deposited on top.

A catastrophe tilted this geologic layer cake, standing the rock layers almost on end, at a 65 degree angle to the northwest. At this steep pitch, the layers slipped apart. Rain water seeped between the cracks. Over eons the layers of iron carbonate rock oxidized creating a band of low phosphorus hematite, a highly prized form of iron ore used in making steel.

You are standing above the “footwall” – the geologic intersection of a dike and the southern most edge of the iron formation. Along this edge the greatest concentration of iron ore was found. This underground wealth, created eons ago, spurred the development of the Penokee Iron Range.
The marker is located at Plummer Headframe Interpretative Park on northbound Wisconsin Highway 77 between Valley Road (to the south) and Plummer Road (to the north), Montreal, Wisconsin 54550.

The Plummer Mine Headframe is the last standing headframe in Wisconsin, and is listed on the National Register of Historic Places.
Other Penokee Iron Range Trail Attractions --
Wisconsin Travel Information Center: State historical marker, displays and photos interpret the history of iron mining on the Penokee Range. A unique outdoor sun dial depicts the dawning and decline of iron mining mining. Cores of solid rock taken from a mine shaft surround the sun dial. State and area travel information. Rest area and picnic sites. Immediately south of the US 2 and Hwy. 51 interchange in Hurley.
Hurley: Plummer Head Frame

This marker is included in the Iron County Heritage Area series of markers. Click here for more information and to view all markers in the series.

These markers are also at this location:

Looking west from the marker location, at the road leading to the headmine.

Lovely nearby lupines . . .

Enter the park at Plummer Mine Road (which does not show up on Google Maps).

Signage on Wisconsin Highway 77,
at the entrance to the road leading to the minehead.

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