Arizona is famous for its canyons and deserts. Arizona's most important geographic feature is the Grand Canyon. Flowing for 1107 km in the state, the Colorado River is Arizona's longest river. Important cities are Phoenix (capital), Tucson, Mesa, Tempe, Glendale, Scottsdale and Yuma. The state population is estimated to be more than 3.6 million. Arizona is the sixth largest state in the United States, with an area of 295,260 km². Arizona, one of the southwestern states, is divided into three main regions: the Colorado Plateau, the mountain region and the desert region. The Colorado Plateau occupies the northern and northeastern parts of Arizona, the mountainous area extends from northwest to the far south, while the desert area covers half of the southwest.