From the point of view of soil-study, Iran can be divided into the following main geological units, from south to north: the platform of Arabia; folded zone; Iranides; central plain; Alburz ranges; and Caspian littoral. This chapter gives a description of the several mapping units, one of which is the soil of the plains and valleys, which includes sand dunes, which are common in most of the arid regions of Iran. Solonchaks and solonetz soils are the saline and alkaline soils of the arid, semi-arid and dry subhumid regions of Iran. A great part of Iran is a plateau about 3,000 ft or more above mean sea-level, containing several types of plateau soils such as grey and red desert soils, Sierozem soil. Palygorskite has been found in the foothills near Dar-i-Khazīneh, in the Kārūn delta in Khūzistān, and in Kirmān.