Mongolia is a location that was to appear in the canceled Fallout Extreme. A band of raiders called the Huns lived in the area.
Because Mongolia was already covered by a large portion of the Gobi desert, the climate in the region would hardly be changed compared to pre-War times.
Before the war, the Gobi Campaign took place here in the Gobi Desert between the US Army and the People's Liberation Army. This may indicate that Mongolia became one of the surrounding Asian countries annexed by China.