Monument Rocks Gallery

The chalk formations at Monument Rocks National Landmark in Gove County are part of the Smoky Hill Chalk Member of the Niobrara Chalk. The massive layers of chalk formed from sediments deposited on the bottom of a great inland sea that covered much of western North America during the later part of the Cretaceous Period, about 80 million years ago. Monument Rocks was designated a National Natural Landmark in 1968.