through Cold Water Cave, the largest and most elaborate cavern system known in Iowa. It is located in northern Winneshiek County, five miles from the Minnesota border. The spring is on land owned by the Iowa Department of Natural Resources since 1943 (managed as part of the Cold Water Creek Wildlife Area), but the presence of the larger cave system was not discovered until 1967. In 1969, a 60-acre tract around the spring was dedicated as a geological state preserve. The spring itself is presently the only part of the cave system that is contained within the state preserve. Part of the cave was designated as a National Natural Landmark in 1987.

Within the preserve, Cold Water Spring issues from the base of a 150-foot-high bluff and flows a short distance into Cold Water Creek, and from there to the Upper Iowa River. The cliff is composed of Galena limestone, a Devonian (375-million-year-old) rock formation. The cave and spring are part of a larger “karst topography,” a term describing a landscape featuring numerous caves, springs, and sinkholes that develop over broad areas underlain by shallowly buried carbonate bedrock. Through time, acidic groundwater seeping along fractures and crevices in the lime-rich rock slowly dissolves openings that can enlarge into passageways and chambers. Karst topography is typical of much of northeast Iowa’s Paleozoic Plateau landform region.