Logan Cave National Wildlife Refuge

There are only two known entry points for the cave: the sinkhole and spring. The sinkhole consists of a steep-sided, funnel-shaped depression about 50 feet in diameter located on a forested hillside. The spring entrance is located on a hillside under an overhang rock bluff. Most of the refuge consists of hillsides which support a mature climax community of oak and hickory.

Groundwater surfacing within the cave forms a stream which flows throughout the cave and at the outfall forms Logan Spring, which drains to Osage Creek just south of the refuge. Osage Creek is a major tributary of the Illinois River, which is the main drainage in southwestern Benton County, and their confluence is about 1.2 miles south of the refuge. In past years, spring water from the cave had a measured flow of approximately 5 million gallons per day and supplied the Logan community, a fish hatchery, and 49 fish ponds.