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Geology of Western Kansas

Smoky Hill River Valley and Lake Scott State Park

The Smoky Hill river valley and its tributaries in western Kansas contain numerous chalk outcroppings or "badlands". They were all part of an ancient inland seaway which extended from the present Gulf of Mexico to Alaska. The placid, semitropical sea averaged 500 ft. deep. Its silty bottom was ideal for fossilization. This prehistoric seabed was drained by the slow uplift of the Rocky Mountains at the end of the Cretaceous period.

Map of Western Interior SeawayThese thick chalk beds have been named the Niobrara formation of the late Cretaceous geologic period and date from 80 to 70 million years old. Chalk is a soft limestone composed mainly of microscopic bits of compacted shells (coccoliths). The Niobrara formation is over 500 feet thick and includes the Fort Hays Limestone at the base and the Smoky Hill Chalk at the top.

Subsequent sediment was deposited during the Tertiary period that followed the Cretaceous. The best known formation of this period is the Ogallala, composed of sandy limy rocks often exposed as bluffs like those at Lake Scott State Park in northern Scott County. The Ogallala formation also provides the majority of groundwater for western Kansas.

During the more recent Pleistocene epoch, glaciers and torrential rains formed most of the present day rivers and streams. It was at this time that the Smoky Hill chalk beds were cut out and continue to erode today, forming pinnacles, spires and unique-shaped forms. Two spectacular examples are Castle Rock in eastern Gove county and Monument Rocks (also known as Chalk Pyramids) in western Gove county. Both sites are inspirational historic landmarks.

Western Kansas is known world-wide for its diverse fossils. The Niobrara formation is famous for its abundance of extinct fossil fish, swimming reptiles (mosasaurs and plesiosaurs), flying reptiles (pteranodons) and ancient birds with teeth (Hesperornis and Ichthyornis). The Ogallala formation yields fossil specimens of rhinoceros, camels, and land tortoises.

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*Information courtesy of Chuck Bonner

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