Cave of the Mounds was accidentally discovered on August 4, 1939. Workers, who were removing high quality limestone from a quarry on the Brigham Farm, blasted into the Cave. The blast tore the face off the quarry and revealed a great underground cavern. All quarrying stopped and never resumed. The dynamite blast revealed a limestone cave more than twenty feet high opening into other rooms and galleries, all containing numerous mineral formations

The story of the geologic formation of the Cave of the Mounds begins with the creation of the rock in which the Cave formed. The Cave was formed within limestone, a sedimentary rock formed from compacted seashells and other marine sediments. This rock dates back Calcite Crystalover 400 million years to the Ordovician Period of the Earth's geologic history. During the Ordovician Period, warm shallow seas covered the continent where we find Wisconsin today. Abundant shell life could thrive in these seas