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Madison County
Low elevation: <400 feet above mean sea level Place: Mississippi River 7.5' quadrangle name: Granite City PLSS: 3-12-9N-10W and 3-35-3N-10W Geology: Cahokia Alluvium in river valleys High elevation: >660 feet above mean sea level Place: Unnamed hilltop 7.5' quadrangle name: Alton PLSS: 3-1-6N-10W Geology: Thin Illinois Vandalia Till over Pennsylvanian Carbondale Formation Area: 732.09 square miles Total relief (approximate): 260 feet Average percent slope: 0.93%
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| Updated 5/4/2007 JKH | |||