Desert mainly refers to the barren land where the ground is completely covered with sand, plants are very scarce, rain is scarce and the air is dry. Desert is also a "sand curtain", an area with drought and water shortage and scarce plants. Desert areas are mostly beaches or sand dunes, and rocks often appear under the sand. Some deserts are salt flats without any vegetation. Deserts are generally aeolian landforms. There are sometimes valuable mineral deposits in the desert, and many oil reserves have been discovered in modern times. There are few residents in the desert, and resource development is relatively easy. The desert climate is dry and it is also a paradise for archaeologists. Many human cultural relics and earlier fossils can be found.