It's what's left of a lake and river.
Also nuke test site.
https://en.wikipedia.org/wiki/Lop_Nur
Also:
>On 17 June 1980, Chinese scientist Peng Jiamu disappeared while walking into Lop Nur in search of water. His body was never found, and his disappearance remains a mystery.
>On 3 June 1996, the Chinese explorer Yu Chunshun died while trying to walk across Lop Nur.