desert in eastern Iran. It stretches about 200 miles (320 km) from northwest to southeast and is about 100 miles wide. In the east a great massif of dunes and sand rises, while in the west an extensive area of high ridges is separated by wind-swept corridors. In its lowest, salt-filled depression—less than 1,000 feet (300 m) above sea level—the summer heat and low humidity are believed to be unsurpassed anywhere.