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1. Patterns of the Park's Landscape
- University of Wisconsin Press
- Chapter
- Additional Information
Jutting into the shimmering waters of Green Bay between Fish Creek and Ephraim lies Peninsula State Park, one of Wisconsin’s most scenic and popular vacation areas. This ,-acre emerald treasure has more than eight miles of shoreline, with sandy beaches and wave-washed rocks, plus a rich mixture of timber, wildlife, colorful undergrowth, and abrupt cliffs. These majestic dolomite outcrops almost attain the quiet dignity of mountains forming an indented arc that runs through the park and parallels the shoreline . Bathed in the golden hue of countless sunsets, the bluffs are the result of momentous events dating back five hundred million years or more. Then, North America lay in the tropics. Over time it has moved slowly northward and rotated ninety degrees counterclockwise to its present location . The continent gradually sank beneath a vast tropical ocean—a large prehistoric extension of the Atlantic Ocean. A broad, bowl-shaped basin centered under present central Michigan subsided more rapidly than surrounding areas, and eastern Wisconsin formed the western rim of that Michigan basin. The first deposits in the ocean were sandstones, followed by shale and limestone from about to million years (Cambrian and Ordovician periods). Later, from to million years (Silurian period), dolomitic limestone was deposited. Countless aquatic shelled animals and corals lived in this warm, Silurian saltwater sea, removing calcium carbonate from the seawater to create their shells and skeletal parts. Farther south, reefs grew on the sea floor. Over the centuries the animals lived, multiplied, and died, creating sediment on the ocean floor. The layers of this buildup of whitish lime, hardened by pressure, heat, and time, slowly formed limestone at the rate of an inch per several thousand years. Eventually this sedimentary rock reached hundreds of feet in atterns of the ark’s andscape thickness. Being more resistant than both under- and overlying strata, it has been eroded to form the prominent Niagara Escarpment—a major landscape feature in eastern Wisconsin. The massive bluffs of Peninsula State Park are part of this dolostone outcropping .The huge Niagara Escarpment bowl forms a gigantic, -mile sickleshaped cuesta extending along the northern shore of Lake Michigan, through Canada’s Bruce Peninsula between Lake Huron and the Georgian Bay, and then jutting across Ontario to Niagara Falls, New York, where it was named. Most of the marine deposition stopped after the Devonian period, around million years ago, and the area started changing to dry land. Eventually, it was subjected to constant erosion, which removed younger layers to expose the Silurian dolostones of the Door Peninsula. Then, about one million years ago, during the Ice Age, massive glaciers began to form in Canada and expand into the region. The last of the several glaciers to move over this area—the Wisconsin stage—came some fifty thousand years ago. This enormous ice sheet, estimated to be a few thousand feet thick in places, had an important role in shaping eastern Wisconsin. Its tremendous weight caused the land to sag and, as the ice reached the northern tip of Door County, it was split by the hard dolostone cuesta. One glacial lobe advanced in a southwesterly direction, forming the Green Bay–Lake ’ The bluffs of Peninsula State Park, along with its more than eight miles of shoreline, are the park’s most distinctive features. (Author’s collection) Winnebago–Rock River lowlands. The other lobe continued southward down the Lake Michigan valley. Beginning about fifteen thousand years ago, a change in climate caused the glacier to gradually recede and melt. As its weight diminished, the landmass of what is now Door County was lifted up and tilted gently to the east. The glacier also helped shape the peninsula, but as the ice sheet retreated northward , ancestral Lake Michigan sculpted the shoreline by forming terraces, wave-cut cliffs, sea caves, graveled beach ridges, and sand beaches. The general configuration of the park evolved into a series of bedrock highlands interspersed with bays of varied depositional material at Fish Creek, Tennison Bay, Nicolet Bay, and Eagle Harbor. As the landmass continued to rise with the reduced weight of the ice, caves cut by lake waves became elevated tens of feet above the present lake level where they can be seen in many of the lakeshore cliffs. Today, evidence of primeval organisms from the Silurian ocean that once covered the peninsula can be found as fossils in the bedrock of the park. The most common and striking in appearance is the honeycomb...
