This sandstone natural bridge, 35 feet high, was carved by the uneven dissolving of mineral deposits holding the sand grains together. After many years of erosion by water, frost action, wind, and gravity, it became the largest natural arch in the state. It remains because of its location in the Driftless Area of southwestern Wisconsin, a region that was not glaciated in the last Ice Age. Beneath the bridge is a natural rockshelter excavated in 1957 by archeologists, who discovered charred wood believed to be from the fire pits of people who may have been here as long ago as 12,000 years, making this one of the oldest dated sites for human occupancy in northeastern North America. These people, called Paleo-Indians, may have hunted animals such as mastodons and wooly mammoths in this area. The rockshelter was first a seasonal and temporary refuge, and later a permanent one. The Native Americans encountered here by white settlers could be regarded as latter-day representatives of this ancient culture.