Flint Hills—Introduction

drawing of outline of this region on Kansas map

Flint Hills--Intro | Flint Hills--Rocks and Minerals
Flint Hills--Places to Visit | Other regions

Download fact sheet on the rocks and minerals of the Flint Hills.

The Flint Hills are familiar to many travelers since this part of the state is traversed by both I-70 and the Kansas Turnpike. Despite disagreement about the exact boundaries of the Flint Hills, most geologists agree that the hills extend from Marshall County, in the north, to Cowley County, in the south. (Of course, the hills don't end abruptly at the state line; they continue into Oklahoma, where they are known as the Osage Hills.)

color photo of hills covered in green grass with white wildflowers

Springtime in the Flint Hills, Chase County.

The Flint Hills were formed by the erosion of Permian-age limestones and shales. During the early part of the Permian Period (which lasted from about 286 to 245 million years ago) shallow seas covered much of the state, as they did during Pennsylvanian times. Unlike the Pennsylvanian limestones to the east, however, many of the limestones in the Flint Hills contain numerous bands of chert, or flint. Because chert is much less soluble than the limestone around it, the weathering of the limestone has left behind a clayey soil full of cherty gravel. Most of the hilltops in this region are capped with this cherty gravel.

Because of the cherty soil, the land is better suited to ranching than farming. Because of this, the Flint Hills is still largely native prairie grassland, one of the last great preserves of tallgrass prairie in the country.

The tall grasses in this region are mostly big and little bluestem, switch grass, and Indian grass. Except along stream and river bottoms, trees are rare. The streams in the Flint Hills have cut deep precipitous channels. Streams cut in chert-bearing strata are narrow, boxlike channels, whereas those cut in weaker shales are wider, more gently sloping valleys.

Text by Liz Brosius, Kansas Geological Survey. Unless noted otherwise, illustrations by Jennifer Sims, Kansas Geological Survey; photographs by John Charlton, Kansas Geological Survey.

Flint Hills--Intro | Flint Hills--Rocks and Minerals
Flint Hills--Places to Visit | Other regions