Natural History:
Illinois Caverns is located in southwestern Illinois in Monroe County about 35 miles south of St. Louis. The entrance to the cave (which also has been known as Burksville Cave, Manmmoth Cave of Illinois, Egyptian Cave and Eckert Cave) is located on a 9.25-acre tract which was purchased by the Department of Natural Resources in 1985.
The process of cave formation involves the power of water over rock. The rocks that form the base of the Illinois Ozark, Shawnee Hills and Mississippi Border Natural Divisions area the sort most susceptible to the forces of water. Millions of years ago huge, shallow seas covered much of this area and deposited many layers of organic and carbonate sediments, forming the limestone and dolomite bedrock that dominate the region today. These types of rocks are easily dissolved and carried off by water, especially along the subterranean cracks or "joints" common to these sedimentary deposits.
Over millenniums of time, the dissolving action of water along the subterranean cracks formed large, water-filled conduits or underground streams. Meanwhile, erosion on the surface began to cut valleys into the surrounding countryside. As the surface valleys deepened, some of the underground passages were drained, creating the air-filled passages known as caves.
During the cave-making process, water acts not only as a dissolver, but also as a builder. In the protected cave environment, dripping and seeping water can deposit carbonate materials and from a host of geological formations.
Natural Features:
Illinois Caverns contains an extensive array of spectacular cave formations, including stalactites, stalagmites, rimstones dams, flowsone, and soda straws. Many of the formations are actively growing with the continued deposition of calcium carbonate.  An underground stream meanders through the cave in its enriched bed. Throughout the year, the temperature in the cave remains a relatively constant 58 degrees Fahrenheit. Approximately 6 miles of the cavern's passages have been mapped by a caving group from Chicago, the windy City Grotto.
In addition to these cave formations, Illinois Caverns is home for a delicately balanced and fragile community of animals. The cave has an outstanding invertebrate fauna, including the largest number of cave-adapted animals known from any cave in Illinois. The cave salamander and at least two species of bats, the little brown and Eastern pipistrel are commonly found in the cave.
