A complex of coalescing ridges and diverse marginal features observed in Mariner 9 pictures of the Hellespontus region of Mars is identified as a dune mass. Many other possible dune features are recognized in mid-latitudes and polar latitudes, and regional differences in the appearance of cratered terrains are attributed to modification by dune deposits. The morphology and temporal behavior of some Martian albedo features can be explained by dune-forming saltation processes. Eolian activity seems to be widespread, if not ubiquitous, on Mars and appears to produce major regional variations in the surface environment.
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