Texas has a variety of landforms including plains, hills, plateaus, and mountain ranges. The plains are flat or gently rolling land while the plateaus are flat elevated land that drop sharply on one or more sides. Texas' rivers and streams eventually flow into the Gulf of Mexico, with most located in East Texas. The major river systems include the Rio Grande, Colorado, Brazos, and Nueces. Texas has few natural lakes but many artificial reservoirs used for water storage and irrigation. Underground aquifers like the Ogallala and Edwards aquifers provide water for homes, farms, and industry across much of the state.