Most of the Caddo historically lived in the Piney Woods ecoregion of the United States, divided among the state regions of East Texas, southern Arkansas, western Louisiana, and southeastern Oklahoma. This region extends up to the foothills of the Ozarks. The Piney Woods are a dense forest of deciduous and pinophyta flora covering rolling hills, steep river valleys, and intermittent wetlands called bayous. Caddo people primarily settled near the Caddo River.