How are coastal dunes and coastal plains similar?

Coastal dunes are a ridge, or a series of ridges, that form at the rear of a beach and differ from most other constructional coastal landforms in that they are formed by the movement of air (aeolian transport) rather than by tidal, wave, or current action. A coastal plain is a flat, low-lying piece of land next to the ocean. Coastal plains are separated from the rest of the interior by nearby landforms, such as mountains. In western South America, a large coastal plain lies between the Andes Mountains and the Pacific Ocean.