The 12th Natural Division is the Ozark Division in southwestern Illinois. (map)
A narrow band from northern Monroe County to Alexander County makes up the Ozark Uplift, a domelike geologic structure of exposed, ancient bedrock centered in the Ozark Mountains of Missouri. Great limestone bluffs mark the edge of the Mississippi Valley. Sandstone ravines in Randolph County and the sinkhole region of Monroe County, with its caves and springs, make this landscape unique in Illinois. This division is divided into three sections. The Northern Section was glaciated during the Illinoian glacial episode and is underlain with relatively pure limestone. The Central Section, which was also glaciated during the same period, is underlain with sandstone. The Southern Section is unglaciated and underlain with cherty limestone. Prior to settlement most of this division was forested and a rich assemblage of tree species can still be found here. This is the only division where shortleaf pine occurs naturally. Hill prairies occurred on the river bluffs of the Northern Section. Unique organisms include the eastern coachwhip snake and the plains scorpion. Visit Pine Hills in Union County and Fults Hill Prairie Nature Preserve in Monroe County to experience this division.