This image shows some of the dunefields of Mars.
Click on image for full size
NASA
Martian Dunefields
This is an example of Martian sand dunes. They are found in the southern hemisphere. They show that wind can change the surface of a planet. Wind is very important to the erosion of the Martian landscape.
Sand dunes were also seen at equatorial latitudes by Mars Pathfinder and also by the Viking I lander in the Chryse Planitia Basin (check the large topographic map of Mars for the distances between these two landing sites).
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