The Flint Hills form a broad band of hills and tallgrass prairie in eastern Kansas that continues into Oklahoma as the Osage Hills. Named for the flint, or chert, left by weathered limestone and shale laid down about 250 million years ago, the region was recorded by Zebulon Pike in 1806. Its rocky, shallow soils made plowing impractical, sparing it from the widespread conversion to cropland that reshaped much of the Great Plains and making cattle ranching the dominant land use. Sustained by annual burns and grazing, the Flint Hills preserve the densest remaining expanse of intact tallgrass prairie in North America and remain a major landscape for conservation and ranching.