The Amir Kabir dam on the Karaj river is a multi-purpose dam that supplies Tehran with hydroelectric power and much needed water. With its sailing and water-skiing facilities, the dam is a popular weekend summer resort. Soil Patterns Soil patterns vary widely. The abundant subtropical vegetation of the Caspian's coastal region is supported by rich brown forest soils. Mountain soils are shallow layers over bedrock, with a high proportion of unweathered fragments.
Natural erosion moves the finer textured soils into the valleys.
These alluvial deposits are mostly chalky, and many are used for pottery. The soil is slightly alkaline and contains three to four per cent of organic material. The saline and alkaline soils in the arid regions are light coloured and infertile. The sand dunes are composed of loose quartz and fragments of other minerals. Except where protect by vegetation, they are in almost constant motion, driven by high winds.