Dasht-e Kavir also known as Kavir-e Namak or Great Salt Desert is a large desert lying in the middle of the Iranian plateau. It is about 800 kilometers (497 mi) long and 320 kilometers (198 mi) wide with a total surface area of about 77,600 square kilometers ( 30,000 mi2), making it the Earth's 23rd largest desert. The area of this desert stretches from the Alborz mountain range in the north-west to the Dasht-e Lut ("Emptiness Desert") in the south-east and is partitioned between the Iranian provinces of Khorasan, Semnan, Tehran, Isfahan and Yazd. It is named after the salt marshes (kavirs) located there.
The Dasht-e Kavir's climate is almost rainless and the area is very arid. Temperatures can reach 50 °C in summer, and the average temperature in January is 22 °C. Day and night temperatures during a year can differ up to 70 °C. Rain usually falls in winter.
The desert soil is covered with sand and pebbles; there are marshes, lakes and wadis. The hot temperatures cause extreme vaporization, which leaves the marshes and mud grounds with large crusts of salt. Heavy storms frequently occur and they can cause sand hills reaching up to 40 m in height. Some parts of Dasht- e Kavir have a more steppe-like appearance.
Vegetation in the Dasht-e Kavir is adapted to the hot and arid climate as well as to the saline soil in which it is rooted. Common plant species like shrubs and grasses can only be found in some valleys and on mountain tops. The most widespread plant is mugwort.