Abandoned Shoreline of Lake Michigan marker - Lincoln Park, Chicago, IL
Posted by: 
adgorn
N 41° 54.932 W 087° 37.960
16T E 447534 N 4640592
Inscribed bronze plaque marking the location of an early beach ridge 8000 to 9000 years ago during the Tolleston phase when the water level of the predecessor of Lake Michigan, called Lake Chicago by geologists, was 20 feet above the current level.
Waymark Code: WM9BC8
Location: Illinois, United States
Date Posted: 07/26/2010
Views: 15
Inscription:
--Abandoned Shoreline of Lake Michigan--
This ridge is an ancient beach or sand bar of Lake Michigan whose waters reached this point 8,000 years ago when the lake level was 20 feet higher than now. Clark Street runs north atop this ridge. The park ponds lie between such old beaches, abandoned by the shrinking lake. The outer boundary of Diversey Harbor and the boat slip running south of it to North Avenue are man-made land. The Chicago Park District
Continued from EarlyChicago: "The undated marker is located in the southern portion of Lincoln Park, on the foot path paralleling the east side of Stockton Drive. A second identical marker is located on the same ancient beach ridge approx 485 feet ENE from the first one.
Lake Chicago (a term used by geologists for a lake that preceded Lake Michigan) was formed when the Wisconsinan glacier retreated from the Chicago area, beginning about 14,000 years ago. Lake Chicago`s level, at its highest, was almost 60 feet higher than the level of present Lake Michigan and the lake completely covered the area now occupied by Chicago. Its northern outlet into the St. Lawrence River was still blocked by remnants of the glacier and it drained through the so-called Chicago outlet, a notch in the Valparaiso moraine, into the Mississippi system. Its western shores reached to where Oak Park and LaGrange now exist. As the glacier shrank in stages, the major three of which are often referred to as the Glenwood phase (50 feet above the level of Lake Michigan; c.12,000 years ago), the Calumet phase (35 feet; c.10,000 years ago), and the Tolleston phase (20 feet; less than 8,000 years ago); each left behind many sandy beach ridges. The lake`s southern shores were dammed by the hills of the Tinley-Valparaiso terminal moraine systems; as the glacier retreated farther and cleared the northern outlet, the lake level fell further and Lake Chicago became Lake Michigan."
I was surprised to find these markers as I walked through the park. Chicago never ceases to amaze!
County: Cook
Historical Society: Chicago Park District
Dedication Date: unknown
Location: Lincoln Park near Chicago's current lakefront
Website: [Web Link]
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