Wang Xiaoli, from the Alshaa League Museum, says this kind of art plays an important role in understanding the prehistoric interactions between the Chinese and their nomadic and pastoral neighbor.

The older generation of scholars, like Ge, believe that some petroglyphs from Inner Mongolia are representations of sun deities. Although the secrets behind these ancient depictions are still waiting to be deciphered, they create a picture of the rich tapestry of human history.

Located between the Badain Jaran and the Tengger deserts, the Mandela Mountains have steep and rugged cliffs, and their black basalt provides a natural canvas for rock art, according to Wang.

It also means danger for fieldwork researchers like Fan, who spends more than eight months a year on the road.

"During these trips, I have had two car accidents and fallen off cliffs three times," Fan says.

He adds that they often get lost, especially during sandstorms, and that the phone signal is weak in the Gobi Desert.

"As most cultural heritage sites can't be reached by road, the movement of facilities and people is challenging. We have to climb the mountains and live in the wilderness," Fan says.

In 2006, Fan's car overturned while he was driving through the Badain Jaran Desert, and an injured colleague had to be sent to the hospital. After taking care of his colleague for three days, Fan finally had time to take a shower.