Date: Formed in the Ice Age during the Pleistocene Epoch (110,000-10,000 years ago), discovered in the 1930s.
Description: This rock is made of granite that was ground into a nearly perfect sphere by glaciers during the last Ice Age. Naturally formed “cannonballs” like these are relatively common in the Sioux City area because it was the southernmost point of glaciation. This example was found in a field near Centerville, SD.
Donor: John Conrad