Guidebook—Geology and Paleontology of Northwestern Kansas

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color photo of white chalk monuments against blue sky

Monument Rocks, Gove County.

Stop 1--Monument Rocks

Monument Rocks is a series of chalk monoliths in western Gove County. Like Castle Rock in the eastern part of the county, Monument Rocks served as a landmark for early travelers and pioneers. It remains a popular tourist site in the Smoky Hill River valley.

Monument Rocks was carved by wind and water in the thick chalk of the Smoky Hill Chalk Member of the Niobrara Chalk (see stratigraphic column). These rocks were deposited during the later part of the Cretaceous Period, about 80 million years ago, when Kansas (and the western United States) was covered by a vast inland sea, several hundred feet deep. Hundreds of feet of shale, limestone, and chalk were deposited on the floor of this relatively shallow sea.

color map of North America showing position of Cretaceous Interior Seaway and other geographic features

Geography of North America during the Cretaceous Period, about 100 million years ago. Present-day Kansas is outlined in red (from Wicander and Monroe, 1989).

color diagram showing position of continents on globe during Late Cretaceous times

Position of the continents during the later part of the Cretaceous Period (Blakey, 2001).

Chalk is a soft, fine-textured form of limestone, composed primarily (90-99%) of calcite. In its pure form, it is white, but it may be colored by iron oxide or other impurities. At Monument Rocks, harder layers within the chalk protect the relatively soft chalk below from erosion, creating the distinctive buttes or monuments. Nonetheless, erosion continues to wear away pieces of these monuments, as was demonstrated by the dramatic toppling of Cobra Rock in 1998 and the collapse of Castle Rock's tallest spire following a thunderstorm in July 2001.

This guidebook is also available in print form as Kansas Geological Survey, Open-file Report 2002-42, from KGS Publications Sales office, 785-864-3965.

Unless noted otherwise, illustrations by Jennifer Sims, Kansas Geological Survey; photographs by John Charlton, Kansas Geological Survey. Text by Liz Brosius, Jim McCauley, Bob Sawin, and Rex Buchanan, Kansas Geological Survey.

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