The main oases of the Governorate (Kharga, Dakhla and Farafra) are located in depressions fallen below the average surface of the desert. These depressions are the result of the combined action of wind, tectonics and water during the Pliocene epoch. They are surrounded totally or in part by a cliff called escarpment or scarp, the top of which is at the level of the normal desert floor. Being the depressions near or at sea level, subterranean water is easily accessible thanks to natural springs or by drilling wells, therefore settlements have been built there since ancient times (Vivian 1990).