The Flint Hills historically known as Bluestem Pastures or Blue Stem Hills, is a region in eastern Kansas and north-central Oklahoma named for the abundant residual flint eroded from the bedrock that lies near or at the surface. It consists of a band of hills stretching from Kansas to Oklahoma, extending from Marshall and Washington counties in the north to Cowley County, Kansas and Kay and Osage counties in Oklahoma in the south, to Geary and Shawnee counties west to east. Oklahomans generally refer to the same geologic formation as the Osage Hills or "The Osage."