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Ogle County
Low elevation: <650 feet above mean sea level
Place: Rock River
7.5' quadrangle name: Grand Detour
PLSS: 4-8-22N-9E
Geology: Cahokia Alluvium in river valley
High elevation: >1020 feet above mean sea level
Place: Southeast branch of Hardpan Ridge
7.5' quadrangle name: Forreston North
PLSS: 4-3-25N-8E
Geology: Thin Illinois Ogle till over Silurian dolomite
Area: 757.12 square miles
Total relief (approximate): 370 feet
Average percent slope: 1.71%
State of Illinois | Illinois Department of Natural Resources | University of Illinois