Short description: Butterfield Overland Dispatch trailmarker near Monument Rocks Natural Area in Gove County. The chalk formations 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 Natural Area was designated a National Natural Landmark in 1968.
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