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Union County
Low elevation: <340 feet above mean sea level
Places: Cypress Creek and Mississippi River
7.5' quadrangle names: Cypress and McClure
PLSS: 3-36-13S-1E and 3-31-13S-3W
Geology: Cahokia Alluvium in river valley
High elevation: >1020 feet above mean sea level
Place: Bald Knob
7.5' quadrangle name: Cobden
PLSS: 3-11-26N-3W
Geology: Lower Devonian hill, the State's biggest, having over 620 feet of relief in a distance of about 1 mile
Area: 417.84 square miles
Total relief (approximate): 680 feet
Average percent slope: 3.15%
State of Illinois | Illinois Department of Natural Resources | University of Illinois