Few places in the country demonstrate the connection between landscape and people better than the tallgrass prairie of the Flint Hills. The hills of the Tallgrass Prairie National Preserve and the surrounding area are shaped by the rocks that lie directly beneath the vegetation and soil— the same rocks which made cultivation difficult and led to the use of native prairie grasses for ranching. This rocky terrain, then, is closely tied to today’s ranching culture. This area, the Flint Hills, is characterized by thin soils, limestone outcrops, vegetation-covered shale intervals between the limestones, deeply incised valleys, and dissected topography. The Flint Hills cross east-central Kansas from the north near the Nebraska border, and extend into Oklahoma to the south. Many of the limestones contain nodules and layers of flint (also called chert)—a hard, dense rock that resists erosion. As the limestones erode, angular fragments of flint accumulate at the surface, giving the Flint Hills their name. The thin, rocky soils and steep slopes of the Flint Hills have precluded cultivation, effectively preserving the native grasslands. Historically, only deep ravines and the floodplains of streams were forested. Most cultivation is limited to river and stream bottoms, such as Fox Creek, just east of the ranch headquarters area; there, the bedrock is covered by a layer of river-deposited sediments that have developed thick soils that are especially valuable for cultivation.
280 Million Year-Old Rocks
Limestone ranges in color from nearly white to brown. It is hard, and much more resistant to erosion than the softer shales, which are usually gray or tan. The alternating beds of limestone and shale produce hillsides with a steplike appearance. Many of the limestone layers create notable benches on the hillsides; the shales form the steep slopes between the benches. The hills themselves are created by a process called differential erosion. Tougher, more resistant limestones and flint cap the tops of hills, while the land between them has been worn away and slowly removed.
The rocks of this area—alternating beds of limestone and shale—were deposited during the Permian Period of geologic history, about 280 million years ago. At that time, the climate here was hot, and the surface was covered by ocean water most of the time. The limestones represent
periods when the region’s surface was covered by shallow, tropical oceans which teemed with life; shales represent times when mud was deposited on the ocean floor. Each of these sedimentary rock layers has been named after towns, creeks, or other nearby landmarks; the names are based on the location where each rock layer was first found and described by geologists.
A closer look at the rock reveals many fossils. Most of these marine fossils are invertebrates—animals without backbones—such as corals, clams, snails, bryozoans (colonies of animals resembling sea fans), sea urchins, crinoids (a stalked animal that is distantly related to the starfish and sea urchin), and clam-like animals called brachiopods. All of these organisms at one time lived in a shallow, warm, tropical ocean. Particularly abundant in some limestones are fusulinids—fossils shaped like wheat grains; these were one-celled animals that floated in the water. When they died, their skeletons drifted to the bottom of the ocean and were preserved in the lime mud of the ocean floor. These lime muds eventually became limestone. Fusulinids can be seen in many of the limestone blocks used for building on the preserve.
Wood was scarce when the prairie was settled primarily by Anglo-American emigrants in the mid-1800s, so the abundant limestone became important for constructing buildings, bridges, and fences. The Cottonwood Limestone, a rock layer that occurs on the preserve near the base of the hills in the Fox Creek valley, is a common building stone in Kansas. The Cottonwood is thick, nearly white in color, even textured, durable, and contains numerous fusulinids. Blocks of stone three or more feet thick, and several feet in length and width, can be taken from a single ledge. The ranch house, portions of the schoolhouse and barn, and many other structures on the preserve are built with Cottonwood Limestone. Many other buildings in the State, including the Chase County Courthouse in Cottonwood Falls, and most of the State Capitol in Topeka, are constructed with Cottonwood Limestone.
The General park map handed out at the visitor center is available on the park's map webpage.For information about topographic maps, geologic maps, and geologic data sets, please see the geologic maps page.
A geology photo album has not been prepared for this park.For information on other photo collections featuring National Park geology, please see the Image Sources page.
A list of publications available about Tallgrass Prairie can be found here.
Parks and Plates: The Geology of Our National Parks, Monuments & Seashores.
Lillie, Robert J., 2005.
W.W. Norton and Company.
9" x 10.75", paperback, 550 pages, full color throughout
The spectacular geology in our national parks provides the answers to many questions about the Earth. The answers can be appreciated through plate tectonics, an exciting way to understand the ongoing natural processes that sculpt our landscape. Parks and Plates is a visual and scientific voyage of discovery!
Ordering from your National Park Cooperative Associations' bookstores helps to support programs in the parks. Please visit the bookstore locator for park books and much more.
For information about permits that are required for conducting geologic research activities in National Parks, see the Permits Information page.
The NPS maintains a searchable data base of research needs that have been identified by parks.
A bibliography of geologic references is being prepared for each park through the Geologic Resources Evaluation Program (GRE). Please see the GRE website for more information and contacts.
NPS Geology and Soils PartnersAssociation of American State Geologists
Geological Society of America
Natural Resource Conservation Service - Soils
U.S. Geological Survey
General information about the park's education and intrepretive programs is available on the park's education webpage.For resources and information on teaching geology using National Park examples, see the Students & Teachers pages.