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Henderson County
Low elevation: ~518 feet above mean sea level
Place: Mississippi River
7.5' quadrangle name: Dallas City
PLSS: 4-34-8N-7W
Geology: Cahokia Allumium, river valley
High elevation: >800 feet above mean sea level
Place: Unnamed hilltop
7.5' quadrangle name: Raritan
PLSS: 4-25-8N-4W
Geology: Thin Illinois Kellerville till upland over Pennsylvanian Carbondale Formation
Area: 391.97 square miles
Total relief (approximate): 282 feet
Average percent slope: 1.04%
State of Illinois | Illinois Department of Natural Resources | University of Illinois