Why is Ili River the only river in China from east to west?

This is the reason for the terrain. The Ili River is located in the Ili Valley in western Xinjiang. The northeast and southeast sides are high and open to the west, so the Ili River flows from east to west.

Ili River straddles China and Kazakstan. Its source, the Tex River, originates from the north side of Hantengli Peak in Tianshan Mountain, flows eastward through Zhaosu Basin and Tex Valley in Xinjiang, China, and then crosses Ishgrik Mountain northward. On the right bank, it joins the tributary Gongnaisi River, which is called Ili River, and flows westward into Horgos River to enter Kazakhstan.

Extended data:

Besides Ili River, some other tributaries may also flow from east to west. For example, the Irtysh River, located in the northern part of Xinjiang, rises in the Altai Mountain in the east, flows into ob river from east to west, flows through Siberia and finally flows into the Arctic Ocean.

There is also Shule River in Hexi Corridor in northern Shaanxi, Gansu Province. Shule River is an inland river, which originates between Tuolai Nanshan and Shule Nanshan in the west of Qilian Mountain. The overall flow direction is southeast to northwest, with a flow of about 580 kilometers. Shule River once flowed into Lop Nur, Xinjiang in prehistoric times. Later, due to the influence of global climate change and human activities, the flow has been greatly shortened and has retreated to Anxi West Lake.

Baidu Encyclopedia-Ili River (Dahe)