At the extreme southern tip of Illinois, the land flattens and is poorly drained. Southern flora is present in this area, the northernmost extent of the coastal plain that stretches to the Gulf of Mexico. The Cache River RRA is located at the southern tip of Illinois. Significant natural features that represent forest, wetland, and aquatic habitats are found at Horseshoe Lake, an old oxbow of the Mississippi River.
American elm grow on the island in the middle of the lake.
Bald cypress, tupelo, swamp cottonwood, willow, and buttonbush are found in the shallow water. The green treefrog is one of the most colorful frogs in North America. In Illinois, the green treefrog is limited to the extreme southern tip of the state. In terms of percentage of the site, the Cache River RRA ranks fourth for grassland, fifth for upland woods, and sixth for bottomland woods. This site has the eighth highest acreage of nonforested wetlands.