Much of southeastern Minnesota's bedrock is limestone. The soluble characteristics of limestone produce a unique geology known as karst topography. Common features of karst regions are sinkholes, springs, disappearing streams, bluffs, and cave systems.
The limestone visible just below the surface in Niagara Cave is that of the Ordovician period. Present within these layers of limestone are the 450 million year-old fossils of aquatic lifeforms that lived in the shallow seas that once covered this region. During the tour you may see cephalopods, fisherites, gastropods, horn corals, or even a trilobite fossil.
The cave system began forming millions of years ago, as water found its way into cracks and crevices in the limestone and slowly widened them, creating passageways that now give us a look into the geology below our feet in this Driftless Region.