The Chalk Pyramids, also known as Monument Rocks, lie in Gove County, Kansas, West of Castle Rock and East of Highway 83. Jutting from the ground, the rocks were carved by erosion from what once was a vast inland sea. They are designated as a National Natural Landmark, the first such location selected by the United States Department of the Interior.
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For a map to this location: Chalk Pyramids/Monument Rocks