The Altai Mountains (Altay Mountains) are a mountain range in Central Asia, where Russia, China, Mongolia and Kazakhstan come together, and are where the rivers Irtysh and Ob have their headwaters. The northwest end of the range is at 52° N and between 84° and 90° E (where it merges with the Sayan Mountains to the east), and extends southeast from there to about 45° N and 99° E, where it gradually becomes lower and merges into the high plateau of the Gobi Desert.