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Generalized Geologic Map of the Conterminous United States
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  The North American Tapestry of Time and Terrain

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Recessional Moraines

  Close-up of
 recessional moraines in northeastern MichiganThe low, arc-shaped ridges just west of the "thumb" region of northeast Michigan are recessional moraines composed of glacial rubble that overlie the Pennsylvanian-age bedrock shown on the map. They mark the northeastward retreat of the Huron Lobe of the last Pleistocene ice sheet from Saginaw Bay about 10,000 years ago. Similar moraines exist south of Lake Michigan, west of Lake Ontario, and in eastern Wisconsin near Green Bay.