Places to Visit—Rock City

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color photo of large spherical rocks in green field in late spring
small drawing of Kansas map with Ottawa County highlighted in red

Ottawa County, Kansas

A few miles south of Minneapolis in Ottawa County is an area covered by huge sandstone spheres, known as Rock City. About two hundred of these unusual rocks, some with diameters up to 27 feet, occupy an area roughly the size of two football fields. Called concretions by geologists, the spheres weathered out of the sandstone in the Dakota Formation, deposited about 100 million years ago during the Cretaceous Period. Over time, ground water circulated through the sandy rock and deposited a limy cement that grew outward in all directions from calcite crystals or limy fossil fragments scattered throughout the sandstone. As the softer uncemented portions of the sandy rock weathered away, these spheres of cemented sandstone remained. The concretions show signs of crossbedding, angled lines that formed in the sand as it was deposited, probably by water currents. Similar sandstone concretions can also be seen at Mushroom Rock State Park in Ellsworth County. Rock City is 3.6 miles south of Minneapolis, off Kansas Highway 106, and can be visited throughout the year. Owned by a local non-profit corporation, Rock City is operated as a public park from May 1 to September 1, when a small admission fee is charged (from The Geologic Record, vol. 9.2).

Other places to visit in the Kansas Smoky Hills.

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