The province stretches from the upper plains of the Chao Phraya river valley, to mountains covered with forests in the west. The Sakae Krang River, a tributary of the Chao Phraya River is the main river of Uthai Thani province. The Huai Kha Khaeng Wildlife Sanctuary at the western boundary to the province Tak and was declared World Heritage in 1991. It covers 2,574 km, and houses almost all of the forest animals of South-East Asia, including tigers and elephants.