From The Earth Story Facebook:
While it certainly looks as though someone has taken a great deal of paint to these hills, these colours in fact formed naturally.
This unique geological formation is known as the Zhangye Danxia landform, found in southern China. It was formed by sediments laid down in a low-elevation fault basin during the Cretaceous period, which then experienced uplift due to their position on top of various fault zones. The various colours are a result of the erosion of the thick-bedded red sandstone and conglomerate: from running water erosion, biological effect, chemical precipitation and organic staining.