Monument Rocks, or the Chalk Pyramids, is a fossil-rich group of chalk formations in western Kansas, about 25 miles south of Oakley in Gove County. Formed around 80 million years ago when this region lay beneath the Western Interior Seaway, the pale buttes, arches, and towers were shaped by erosion from marine carbonate deposits rather than volcanic or mountain-building forces. Some rise about 70 feet, creating one of the plains' most striking geologic landmarks. Recognized for both scenic beauty and scientific value, Monument Rocks became Kansas's first National Natural Landmark and later, with nearby Castle Rock, one of the Eight Wonders of Kansas.