At 160 acres, Kalsow Prairie is one of Iowa’s largest remaining virgin prairies. This state preserve is an 8,000 year old remnant black-soil tallgrass prairie that was never plowed. Kalsow Prairie is believed to be the center of the 74 million year old Manson impact structure. This structure was formed when a 12-trillion ton meteorite 1.5 miles in diameter struck the earth, igniting most of Iowa and killing most animal life within a 650 mile “death ring” from Denver to Detroit. Today it lies invisible 100 to 300 feet beneath the glacial deposits. The virgin prairie has many small potholes which are remnants of the last glaciers. Hydrophytes or water plants grow in these wet spots, providing diversity. At least 20 species of mammals live here, including the short-tailed shrew and jumping mouse. Look for a variety of butterflies and birds. Leopard and cricket frogs can be heard in the potholes. Smooth green snakes and northern prairie skinks have also been found here.