Claim: Eagle Cave is an onyx cave that was discovered in 1849,in Richland County, Wisconsin, United States.
Evidence: 1849 Onyx Richland County, Wisconsin, United States 
Eagle Cave is known as Wisconsin's largest onyx cave and was the first cave to be commercially owned and operated in Wisconsin. The cave was discovered in 1849 and opened to the public in 1938. Eagle Cave is an onyx cave located near Blue River, Wisconsin, in Richland County, Wisconsin, United States.