 |
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%
State of Illinois | Illinois Department of Natural Resources | University of Illinois