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Jackson County
Low elevation: <340 feet above mean sea level
Place: Big Muddy and Mississippi Rivers
7.5' quadrangle name: Neelys Landing
PLSS: 3-11-11S-4W
Geology: Cahokia Alluvium in river valley
High elevation: ~811 feet above mean sea level
Place: Grassy Knob
7.5' quadrangle name: Wolf Lake
PLSS: 3-34-10S-3W
Geology: Loess hill over Lower Devonian carbonate bedrock
Area: 599.01 square miles
Total relief (approximate): 417 feet
Average percent slope: 2.25%
State of Illinois | Illinois Department of Natural Resources | University of Illinois