Crystal Cave is a cave located in Wisconsin’s Pierce County, near the Town of Spring Valley on Highway 29. The cave was discovered in 1881 by local brothers George and William Vanasse. Crystal Cave is a multi-level solutional cave formed in dolomite bedrock in the Prairie du Chien group. The dolomite was formed 485 million years ago during the Lower Ordovician Period when a warm shallow ocean covered much of Minnesota and Wisconsin. It s Wisconsin’s longest known cave.GeologyCrystal Cave is a multi-level maze type of solutional cave consisting of three levels. It extends to a depth of 69 ft. (21 m.) and is 4600 ft. (1.4 km.) in length, contained completely in the Prairie du Chen group. The bedrock forming the cave walls formed during the Ordovician Period. The third level is the most extensive of the three, having developed along existing Northeast to Southwest trending joints in the bedrock. Dating the period the cave began to form has proven difficult because of erosion by glacial waters and the deposit of debris during the Wisconsin Glaciation from the nearby terminus of the Laurentide Ice Sheet's Superior lobe. The commonly accepted theory of the cave's formation is that it was formed by a weak carbonic acid solution formed from rainwater and snowmelt that mixed with biogenic carbon dioxide found in the topsoil, which then infiltrated existing joints and fractures in the bedrock, expanding them into the openings that make up the cave’s passageways. Some have advanced that the cave's formation is actually hypogenic in origin.
