Ad-Dahna Desert passages which can be several kilometers long. Local Bedouin have always known these caves and some were used as water supplies. They were first systematically studied in the 1981, and later explored and reported by the Saudi Geological Survey. Ad-Dahna Desert The ad-Dahna Desert is the central division of the Arabian Desert. It is a corridor of sandy terrain forming a bow-like shape that connects an-Nafud desert in the north to Rub' al-Khali desert in the south. Its length is more than 1,000 km siding Twaik Mountains from the east and does not exceed 80 km in width. It is
High Desert (Oregon) level. To the east, the high desert country of the Columbia Plateau extends across the Snake River and into Idaho. A number of rivers flow through the high desert region. These include the Deschutes River and its tributary the Crooked River, as well as the Malheur, Owyhee, and John Day rivers, which are all within the Columbia River watershed. Because the high desert encompasses the portion of the hydrographic Great Basin located in Oregon, smaller rivers in the high desert flow into closed basins. The Chewaucan River, the Donner und Blitzen River, and the Silvies River each flow into some