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

fusilinids—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. Fusilinids can be seen in many of the limestone

blocks used for building on the preserve.

Nebraska

Kansas

Oklahoma

Missouri

Flint Hills

Colorado

0 0

80 120

N

Few places in this country demonstrate the connection between

landscape and people better than the tallgrass prairie in the Flint

Hills. The Flint Hills 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 is closely tied to

today’s ranching culture. The Flint Hills region 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 flood plains of streams were

forested. Most cultivation is limited to river and stream bottoms, such

as along 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.

Layers of Ocean Floor

Abundant Fossils

Flint Hills

Courtesy of KS Geological Survey

Courtesy of KS Geological Survey

Courtesy of KS Geological Survey

Limestone ranges in color from nearly white to brown. It is hard, and

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 terraced 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 locations where

each rock layer was first found and described by geologists.

N

0

0

80

120

Geology and the Prairie

National Park Service

U.S. Department of the Interior

Tallgrass Prairie National Preserve

Strong City, Kansas
Classification of Rocks at the Tallgrass Prairie

National Preserve

Members Formations

Fort Riley

Limestone

Barneston

limestone

Florence

Limestone

Blue Springs

Limestone

Kinney

Limestone

Wymore

Shale

Matfield

Shale

Schroyer Ls.

Havensville Sh. Wreford

Limestone Threemile

Limestone

Speiser

Shale

Funston

Limestone

Blue Rapids

Shale

Crouse

Limestone

Easly Creek

Shale

Middleburg Ls.

Hooser Sh.

Eiss Ls.

Morrill Ls.

Florena Sh.

Cottonwood Ls.

Steams

Shale

Bader

Limestone

Beattie

Limestone

Eskridge

Shale

Feet

0

40

Permian Period

Oketo Sh.

Threemile Limestone forms a prominent bench on the

hillsides and caps the tops of the hills on the south end of

the Preserve.

Florence Limestone is found at top of the

highest hills on the northern end of the

Tallgrass Prairie National Preserve. A large

amount of flint occurs at this level.

The massive, tri-level barn

is built mainly out of

Crouse Limestone.

Cottonwood Limestone is the primary building material used in

the construction of the preserve’s three-story mansion.

For additional reading: • Kansas Geology: An Introduction to Landscapes, Rocks, Minerals, and Fossils

Edited by Rex Buchanan, University Press of Kansas, 1984.

• Ancient Life Found in Kansas Rocks: An Introduction to Common Kansas Fossils

by Roger B. Williams, Kansas Geological Survey, Educational Series I, 1975.

• Konza Prairie: ATallgrass Natural History by O.J. Reichman, University Press of Kansas, 1991.

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 fusilinids. 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 were built with Cottonwood limestone. Numerous

buildings in the state, including the Chase County Courthouse

in Cottonwood Falls, and most of the State Capitol building in

Topeka, were constructed with Cottonwood limestone.

Building With Limestone

This publication was

developed through

cooperation with the

Kansas Geological Survey.