Designated a NNL in 1968, Monument Rocks Natural Area includes pinnacles, small buttes, and spires of the Niobrara formation standing as much as 60 feet above the plain. These erosional remnants of sediments deposited in the ancient Kansas Sea of Cretaceous time, are striking illustrations of differential erosion of soft chalk beds overlain by a more resistant cap of limestone.
U.S. National Park Service
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