Duns are flat-bottomed valleys that are formed between the Shivalik hill and the lesser Himalayas. They are formed as a result of folding when the Eurasian plate and the Indian plate collide. The valleys are accumulated with coarse alluvium passed down by Himalayan rivers. Duns are usually established under the Himalayan River with coarse alluvium present with it. They are narrow and are made of alluvial soil and gravel. Duns are also known as Dims and are used as a local word for valley or open valley. They are generally 8-10 km wide and up to 40-50 km long. Some examples of duns include Kotli Dun, Dehra Dun, and Patli Dun.