This is a photograph of Castle Rock located near the Smoky Hill River in Gove County, Kansas. Castle Rock was a landmark on the Butterfield Overland Dispatch route. The chalk was deposited in the area by an ancient inland sea. The formation was formed by the weathering of the chalk by wind and water. It received its name because it is said to look like a castle rising above the prairie. Alexander Gardner photographed the Union Pacific Railway, Eastern Division, as it was being built across Kansas. Along the route, he documented towns, forts, rivers, wildlife, plants, and landscape. This image is from a series Across the Continent on the Kansas Pacific Railroad.