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Dunes are piles of granular material that have been deposited by wind and water into hills or long ridges. Dune formation begins with a process called saltation, in which the flow of sand across the desert floor is interrupted by an obstacle that blocks the sand's movement. It then begins to accumulate and eventually to form a hill. The heights of dunes may be shallow, or they may grow up to 500–600 feet (150–180 meters). Most dunes are sand, but white gypsum dunes are found in southern New Mexico's Tularosa Valley at White Sands National Monument. Rarely, dunes may be composed of tephra, shell fragments, or heavy minerals such as magnetite.

Dunes are sculpted by the winds into different kinds of shapes. Transverse linear dunes are ...

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