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Putnam County
Low elevation: ~440 feet above mean sea level
Place: Illinois River
7.5' quadrangle name: Henry
PLSS: 3-33-31N-2W
Geology: Cahokia Alluvium in river valley
High elevation: >740 feet above mean sea level
Place: Unnamed hilltop
7.5' quadrangle name: McNabb
PLSS: 3-17-32N-1W
Geology: Mount Palatine Moraine
Area: 170.51 square miles
Total relief (approximate): 300 feet
Average percent slope: 1.77%
State of Illinois | Illinois Department of Natural Resources | University of Illinois