This color-infrared image shows sand dunes in Melas Chasma, located within the Valles Marineris canyon system. The dark-blue and purple colors indicate coarse-grained sands that are comprised of basalt, an iron and magnesium-rich volcanic rock that formed from cooled lava millions of years ago when volcanism was an active process on Mars.
Migrating sand dunes often lead to the erosion and excavation of underlying material; regions where there are active dune fields are ideal places to search for exposed bedrock. Repeated imaging of dunes may also show changes that provide evidence for active surface processes related to wind patterns and climate.
More information is available at https://photojournal.jpl.nasa.gov/catalog/PIA22783