The Helan Mountains, frequently called Alashan Mountains in older sources, are an isolated desert mountain range forming the border of Inner Mongolia's Alxa League and Ningxia. They run north-south parallel to the north-flowing Yellow River in the Ordos Loop section. The river is mostly east of the mountains, but in the north it crosses without making a significant gorge and flows on the west side. To the west lies the extremely arid Tengger Desert, while to the east is an irrigated area beside the Yellow River, in which lie the cities of Yinchuan and Shizuishan - a little further east of which lies the Mu Us portion of the Ordos Desert. To the north lies the Inner Mongolian city of Wuhai.

They are about 200 kilometres (120 mi) from north to south, from 15 to 50 kilometres (9.3 to 31.1 mi) wide and average about 2,000 metres (6,600 ft) in altitude (the Yellow River here is about 1,100 metres (3,600 ft) above sea level). Their highest peak is 3,556 metres (11,667 ft).