But why are the dunes in Proctor Crater so dark when the surrounding landscape appears to be scattered with brightly colored boulders and smaller dunes?
"The dark dunes are composed of basaltic sand that has collected on the bottom of the crater," remarks to Maria Banks, a geologist and planetary scientist from the University of Arizona.
It would appear that these large dunes were formed recently as they overlay the brighter rippled landscape. Basalt is formed as a product of volcanic activity, but over the eons, Mars' winds have eroded this rock into fine basaltic sand, eventually creating these dramatically contrasting sand dunes.
For more assorted Mars dunes, browse through the HiRISE database.
Sources: Universe Today, HiRISE
Image credits: NASA/JPL/University of Arizona