These hills in Gansu province, China, look as though someone has painted them with stripes. The colours are real.

Over millions of years, layers of sandstone and other sediments were laid down, each with different minerals — iron compounds can turn rock red or yellow, for example. Then the movement of tectonic plates — the same collision that pushed up the Himalayas — tilted and folded the layers, and wind and rain eroded them into ridges, exposing the stripes.

The colours are strongest after rain and in the low light of early morning and evening. The area is part of a geopark and part of the "China Danxia" landscapes that were named a UNESCO World Heritage Site in 2010.