It is bounded by the Tian Shan to the south, the Altai Mountains to the northeast and the Tarbagatai Mountains to the northwest. The three corners are relatively open. The northern corner is the valley of the upper Irtysh River. The western corner is the Dzungarian Gate, a historically important gateway between Dzungaria and the Kazakh Steppe; presently, a highway and a railway (opened in 1990) run through it, connecting China with Kazakhstan. The eastern corner of the basin leads to Gansu and the rest of China. In the south, an easy pass leads from Ürümqi to the Turfan Depression. In the southwest, the tall Borohoro Mountains branch of the Tian Shan separates the basin from the upper Ili River.