The Danxia landform is a unique type of “petrographic geomorphology” found in China, characterized by strips of red sedimentary rock in steep cliffs. According to Wikipedia, “the landforms look very much like karst topography that forms in areas underlain by limestones, but since the rocks that form danxia are sandstones and conglomerates, they have been called "pseudo-karst" landforms.” A very peculiar feature of danxia landscape is the development of numerous caves of various sizes and shapes. The caves tend to be shallow and isolated, unlike true karst terrain where caves tend to form deep, interconnecting networks.
The word “Danxia” actually comes from Mount Danxia, located in Renhua County of Guangdong Province, where the most famous examples of the Danxia landform is seen. Over the past 70 years, geologists and geographers have identified over 700 Danxia landforms in China, mostly in southeast and southwest China. Today, the study of Danxia landforms has developed into a sub-discipline of geomorphology and Danxia Mountain has become China’s research base for Danxia landforms.
Danxia landform’s rock walls and cliffs are formed of red sandstone and conglomerate. About 100 million years ago, there used to be a huge inland basin here full of silt carried by the waters from the surrounding mountains. With the rise in global temperature the basin dried up and in these arid conditions the sediment oxidized and turned rust color. Some 30 million years later a 3,700-meter-thick red-colored layer formed on the basin, known as the chalk bed. On the top, there was a 1,300-meter-thick solid layer formed during the Cretaceous period, from which the peaks of Danxia Mountain gradually took shape. During the next 30 million years orogenic movement has lifted the whole basin many times. Water flowing down through fissures cut through and eroded the sedimentary rock, the slope broke and receded, leaving behind the red fragmentary rocks we see now. Orogenic movement is still going on in the Danxia Mountain area, with an average rise of 0.87 meter every 10,000 years over the last 500,000 years.
In 2010, six Danxia landscapes were inscribed as World Heritage Sites.