Definition

The Niagara Escarpment is a prominent rock ridge that spans nearly 1,000 miles in an arc across the Great Lakes region, forming the ancient “backbone” of North America. It runs from eastern Wisconsin to the Upper Peninsula of Michigan, through southern Ontario to western New York State, where Niagara Falls cascades over it, giving the escarpment its name. The red line on this map shows the path of the Niagara Escarpment.

NewGreatArcMap_June2016

In Wisconsin, the Niagara Escarpment is a discontinuous ridge that stretches about 250 miles from Waukesha County north to Rock Island at the tip of Door County.  It is highest along the western edge of Door County, where it reaches a height of about 250 feet above Green Bay.

So what exactly is an ‘escarpment’?  An escarpment is the steep cliff edge of a cuesta, which is formed from slightly tilted layers of rocks.  The steep cliff face forms when crumbly rocks, such as shale, are eroded from beneath erosion-resistant rocks like limestone or dolomite, which then break off to make the cliff face.

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The rocks of the Niagara Cuesta were tilted when the Earth’s crust sagged, forming a bowl-shaped depression beneath Michigan. The Niagara Escarpment is the exposed, up-tilted, outer edge of this feature. The lands behind (to the east in Wisconsin’s case) are referred to as the Niagara Cuesta. A cuesta, or sometime referred to as a ‘dip-slope’, is the term used to describe the lands located behind an escarpment. The Niagara Cuesta is comprised of the same underlying highly fractured bedrock, some of which is close to the surface and contains karst features. More about karst and its interactions with the groundwater system can be found here.

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www.hamiltonnature.org

As many readers know, the Niagara Escarpment is a technical geology term to describe this landscape feature, however; many area residents – depending on where they live – simply know of it as either “The Ledge” or “The Bluff”.  Interestingly enough, in the Hamilton, Ontario area, the escarpment is referred to as “The Mountain” (even though it’s technically not a mountain).