More than 480 caves occur in Illinois. The caves of the Sinkhole Plain in Monroe and St. Clair counties are the most numerous and interesting in the state. In Illinois, caves are found in areas of major limestone or dolomite outcrops called karsts. A few animals have adapted to the dark, cool and humid environment of the deep caves. Some are both blind and colorless, such as isopods, amphipods, pseudo-scorpions, and springtails.

SIZE: 291,305 acres; 455 square miles

LOCATION:Southwestern Illinois along the Mississippi River near St. Louis; Madison, Monroe, Randolph, and St. Clair counties.

The Karst/Cave Area RRA includes Mississippi bottomlands and part of the Ozark plateau. Exceptional features are its limestone bedrock, numerous caves and sinkholes, old growth forest, and unique flora and fauna. The area originally contained large areas of forest, prairie, and wetland.

Of the twelve species of bats that occur in Illinios, nine are called cave bats because they generally hibernate in caves or abandoned mines. A Monroe County cave is one of two known hibernation sites of the federally endangered Indiana bat. Gray bats, also a federally endangered species, are limited in Illinois to southern and west-central parts of the state where there are numerous caves. Two other species, the southeastern bat and Rafinesques's big-eared bat, are endangered in Illinois and are only found in the southernmost part of the state.

LANDCOVER : This RRA is half cropland and one-fourth wooded. It has relatively moderate percentages of upland and bottomland woods. This site ranks second in acreage and seventh in percentage of nonforested wetlands among the 30 RRAs.

NATURAL AREAS : The Karst/Cave RRA has the second highest acreage of Natural Areas. Over nine percent of this large site is covered by Natural Area sites. Of the 27 Natural Areas, seven sites are larger than 1,000 acres. Significant natural features are caves, hill prairies, springs, marshes, herpetological areas, and rookeries.

BIOLOGICALLY SIGNIFICANT STREAMS : Designated BSS streams in this RRA include a short length of the Mississippi River and a tributary to Horse Creek, which total 2.9 miles.

HERITAGE SITES : A moderate number of Heritage sites (92) occurs here. Eight significant communities types occur here along with nine plant species, 18 animal species, and two rookeries. There are 14 cave occurrences.

STATE AND FEDERAL LAND : Horseshoe Lake State Park and Kaskaskia State Fish and Wildlife Area are the only state or federal land in this site.

NATURE PRESERVES : There are four Nature Preserves in this site. High quality terrestrial cave and aquatic cave communities, hill prairies, and old growth forest remnants are important natural features of these preserves.

NATURAL DIVISIONS : Five natural divisions comprise this RRA. Most of the area is Lower Mississippi River Bottomlands (43%), Ozarks (28%), and Southern Till Plain (18%). Over a third of the state's Lower Mississippi River Bottomlands Division and 20% of the Ozark Division occurs in this RRA.