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Door County and the Niagara Escarpment

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The Niagara Escarpment is a geological foundation that stretches from New York state through Niagara Falls (where it got its name) then through the Bruce Peninsula (which splits the two lobes of Lake Huron), across the lower part of Michigan’s Upper Peninsula, defines the geography of Door County and continues through the east side of Lake Winnebago and the Horicon Marsh to terminate in northern Illinois, where it is no longer visible. Not to be too technical, the Escarpment was formed when glaciers one to two miles thick gouged out soft shale and left harder dolomite exposed. These glaciers gave shape to the Great Lakes, the world’s largest single supply of fresh water.

When mapping probable geologic changes in our area, a hypothetical map shows the ancient Peshtigo and Menominee Rivers (now emptying into Green Bay from the west side) flowed through what is now Sturgeon Bay into the Michigan River. The Michigan River was further gouged out by the glaciers to become Lake Michigan.

Door County’s Green Bay side has the true escarpment with exposed dolomite rock 200-250 feet high. At the base of these rock faces are remnants of the chunks of stone that fall from the cliffs to form “talus.” The talus has a whole sensitive ecosystem that can be degraded by overuse and too many people wanting to view the wonders found there. Some of the oldest living trees in all of the Midwest, some are almost 1200 years old, are found on the Escarpment. These trees are the deformed, barely alive, white cedars found on the rock cliffs. Interestingly, the same tree growing in optimum conditions lives only 1/3 as long as the “cliff hangers.”

In Door County, the landscape slopes downward to the Lake Michigan side in what is known as a “cuesta,” or a “dip slope plain” in geology speak. Generally on the Lake side there are sand beaches and the shallow inland lakes that are the remnants of glacial bays that have filled in over time. We have two different coastal water characteristics in our little County and over 241 rare species, including the Hines Emerald Dragonfly, several species of orchid, ferns and salamanders.

The Mink River Estuary is a model of a coastal wetland that has been conserved by a coalition of preservation organizations. Early settlers thought there were tides on the estuary, but the changing water levels are the result of “seiche” activity that is the result of winds blowing water into and out of Rowleys Bay and up the estuary.

The plants growing in the talus on the Bay side can be disrupted by a single hiker, chemicals used on crops will show up in drinking water the next day and roads built too close to the edge of fragilebiosystems have far reaching consequences. The land of the escarpment, and especially in Door County, is a very fragile ecosystem. The bedrock, without the benefit of a natural soil filtration system, allows water to run freely — it takes less than 24 hours for water to reach Lake level.

One of our challenges is to allow residents and visitors to enjoy our natural allure “up close and personal” without destroying that allure by over use.



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