Why are most of the mountains in Leshan red?

The closed basin topography and sharply reduced water surface make the climate gradually dry and hot, and the sediments change from marine phase and land-sea alternating phase to continental phase. A large number of weathered, eroded and denuded materials have accumulated thousands of meters thick in the basin, forming purple sand, mud and shale.

/question/30377927.html？ an = 0 & ampsi=3

Not only the mountains in Leshan are red, but also many mountains in Sichuan are red.