House, Scott (May 14, 2005). "Fact Sheet on 6000 Caves". The Missouri Speleological Survey. Archived from the original on May 9, 2008. Retrieved March 16, 2008.
House, Scott (May 14, 2005). "Fact Sheet on 6000 Caves". The Missouri Speleological Survey. Archived from the original on May 9, 2008. Retrieved March 16, 2008.