• The setting sun over the Flint Hills casts shadows across the wide expanse of tallgrass prairie.

    Tallgrass Prairie

    National Preserve Kansas

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Geology in the Flint Hills

The limestone and shale sediments seen in the Flint Hills today show us a cross section of a landscape that looked much different long ago.

courtesy of Inland Sea Productions

The Flint Hills Geology

Except for catastrophic events such as volcanoes, floods, and earthquakes, much of the Earth’s geology has been created at an imperceptibly slow pace. Millions of years are often required to produce the landscapes we see today throughout the world.

Tallgrass Prairie National Preserve is located in the heart of the Flint Hills region of Kansas. This physiographic region extends from the Nebraska state line southward into northern Oklahoma and is from 30 to 100 miles wide. The hills are usually flat topped with concave slopes that have developed on the underlying limestone and shale layers.

The Kansas of today was once the bed of a vast shallow body of water called the Permian Sea. During this extensive time period, the earth’s oceans rose and fell many times creating different types of aquatic environments. The shallow warm seas supported enormous numbers of invertebrates, fishes and amphibians.

Many animals and plants (such as oysters, corals, some sponges, sea urchins, plankton, and algae) take calcium carbonate (CaCO3) out of the water and secrete it to form shells or skeletons. As these organisms die, they drop to the ocean floor. Over time the organic parts decay and the calcium carbonate accumulates to form limestone. The limestone and shale sediments seen in the Flint Hills today show us a cross section of a landscape that looked much different long ago.

It can be difficult to imagine that the prairie grass was once the mucky bottom of a vast inland sea. If Kansas appeared today as it did 250 million years ago, things would be very different. We would need boats rather than automobiles to get around. Instead of agriculture, fishing might be the main economic industry. In fact most of Kansas would be under water! No reason to build these beautiful limestone buildings. Tallgrass Prairie National Preserve offers us all an opportunity to study this amazing prehistoric past up close, (and on dry land).

Geologic Map of the Preserve

Did You Know?

Aerial photo of the Flint Hills at Tallgrass Prairie National Preserve

Kansas was once the bed of a vast inland sea. The unique, stairstep landscape of the Flint Hills was formed through a process of differential erosion. Erosion washed away the soft shale layers and left the tougher layers of limestone and flint to form the hilltops and prominent benches.