Chuluut River in Undur-Ulaan Soum in Arkhangai province comes from mountain Eg of the Khangai mountain range and flows about 415km, forming river Selenge, the biggest river of Mongolia, by joining Delger River and Ider River. Chuluut River flows through 20m-deep steep canyon of basaltic rock for about 100km from the river-mouth of Teel River till Atsat River. A basaltic rock is magma flew from the volcano Khorgo and other volcanoes near it. There is a small waterfall flowing down from a steep rock near a confluence of Suman and Chuluut rivers. This waterfall is known as Choidogyn Borgio and it is interesting to see fish gathered from Chuluut and Selenge rivers flashing the surface upwards waterfall. Chuluut River canyon is rich with springs of hydro carbonate, sulfate and sodium, and contains many petro glyphs date back to Neolithic and Bronze Age. These cave paintings include unique depictions such as images of 6 women giving a birth, a man shooting with a bow and an arrow, herds of ibex and deer, a man standing with raised hands, oxen, mountain sheep, profiled paintings of men and a masked man. These paintings were taken under state protection in 1998.