Gitchie Manitou is a 91-acre preserve best known for a natural outcropping of Sioux Quartzite. It is located in the extreme northwest corner of Iowa in Lyon County, just southeast of the suburbs of Sioux Falls, South Dakota. In 1916, the state of Iowa purchased the first 47.5 acres for use as a quarry, but later transferred the area to the Board of Conservation. The area was initially classified as a state park, and later a “preserve.” It was formally dedicated as a geological, archaeological, historical, and biological state preserve in 1969. The preserve was named after a Sioux Indian name meaning “Great Spirit” or “Great Force of Nature.” Geologically, the preserve contains distinctive rock outcroppings of smooth, wind-polished, pink-colored Sioux Quartzite. At 1.6 billion years old, this is the oldest bedrock that can be seen at the land surface anywhere in Iowa. These outcrops are part of a 135-mile-long, east-westtrending ridge of ancient bedrock whose main axis extends from New Ulm, Minnesota, to Mitchell, South Dakota. The Iowa outcrops lie along the southern flank of this buried ridge. The name “Sioux Quartzite” was assigned to the rock unit by geologist Charles White in 1870 from the exposures at this site. Thus, Gitchie Manitou State Preserve contains the designated “type section” of the Sioux Quartzite, where its defining features were first described in the geological literature. From the 1890s to 1920, quartzite was quarried from what is now the northeast corner of the preserve. The quarry is now filled with water and is called “Jasper Pool.” Archaeological features of the preserve include seventeen conical mounds in the southern portion of the preserve and several Woodland or Great Oasis habitation sites. Further research is needed to understand the significance of these sites, which may be part of a larger complex including nearby Blood Run Historic Landmark.