Due to strong wind erosion, the fine sand and dust in the original floodplain are removed, and the ground is covered by heavier gravels of various sizes. This landscape is called a ‘gravel desert’ or gobi. The two main types of gobis are debris stone gobis and gravel gobis. They can be found in the northwestern part of Yumen, the Taklama Basin, Junggar Basin, the edge of the Qaidam Basin, the Hexi Corridor and the western part of Inner Mongolia. The gravels in the Gobi Desert have developed due to the abrasion of sand carried by the wind, which in turn formed angular aragonite, and the surface is often covered with oily dark brown desert rock paint.