The 6th Natural Division is the Illinois River and Mississippi River Sand Areas, encompassing much of Mason County as well as parts of Whiteside, Henderson, Woodford, Peoria, Putnam, Tazewell, Cass and Scott Counties.(map)
The sand areas and dunes in the bottomlands of the Illinois and Mississippi rivers comprise this division. Dry sand prairie and scrub oak forest, dominated by black and blackjack oak, are the natural vegetation. The division is divided into two parts—Illinois River and Mississippi River sections. The meltwaters of the Wisconsin glacial episode greatly affected the formation of both the Havana sand deposit (Illinois River) and the Hanover-Oquawka sand deposit (Mississippi River). The Havana sand was formed as meltwater cascaded down the prehistoric course of the Illinois River. The Hanover-Oquawka deposit occupies an expanse between the bluffs on the east and the Mississippi River on the west. In both of these areas, tremendous floods carried a huge volume of sand and gravel downstream at breakneck speed, depositing material when the water slowed. Look for prickly-pear cactus, three-awn grass, little bluestem, and Indian grass in Sand Ridge State Forest or Thomson-Fulton Sand Prairie Nature Preserve.