Dip Slope, West Shore of Green Bay

Steven Dutch, Natural and Applied Sciences, University of Wisconsin - Green Bay
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Above: the Door Peninsula is a classic cuesta, a landform created by a dipping resistant rock layer. The Silurian rocks (yellow) slope gently east into Lake Michigan with a dip of less than a degree. The land surface is a somewhat beveled and drift-covered dip slope. The western edge of the Silurian cuesta is the drainage divide, so most streams flow east away from the escarpment. As a result there are few waterfalls on the escarpment.

Under the Silurian rocks are the softer Maquoketa shales, which were scoured away by the glaciers to create Green Bay and the Fox River lowland. West of Green Bay, the shales were completely scoured away and the next series of resistant rocks, the Sinnipee Group of dolomites, was exposed. These rocks also form a cuesta, although it is not obvious because it is heavily camouflaged by glacial deposits.

If you drive north along US 41-141 past the southwest corner of Green Bay, it's easy to get the impression that the western shore of the bay is all swamp and wetland. In fact, the cover of glacial deposits west of the bay is quite thin and there are even a few outcrops along the shore. Numerous natural outcrops were exploited as quarry sites.

The geologic map above shows quarries in the Sinnipee Group dolomites with black X's. Note that some are within a very short distance of the shore.

The chain of four quarries in Howard (1 on the map above) just a short distance from the mouth of Duck Creek are the most obvious expression of near-surface bedrock along the bay shore. This panorama was made in 1999, before the largest and most recently active quarry was closed and began flooding. At the far north end of the quarry are natural, glacially striated exposures. The southeastern corner of the quarry also exposes striated pavement, but the best outcrop area has been covered for a number of years.

Entrance to a quarry in Little Suamico (2 on the map above).
Glacially striated rock in an abandoned quarry east of Abrams (3 on the map above). Below are views of the quarry and outcrops.

Just east of the quarry on Oak Orchard Road, we find a rocky shoreline. Although there doesn't appear to be actual outcrop in these pictures, the rocky slabs on the beach testify to bedrock either offshore or beneath the beach.

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Created 3 May 2005, Last Update 14 Apr 2007

Not an official UW Green Bay site

	Entrance to a quarry in Little Suamico (2 on the map above).
	Glacially striated rock in an abandoned quarry east of Abrams (3 on the map above). Below are views of the quarry and outcrops.


	Just east of the quarry on Oak Orchard Road, we find a rocky shoreline. Although there doesn't appear to be actual outcrop in these pictures, the rocky slabs on the beach testify to bedrock either offshore or beneath the beach.