In some areas, dune fields composed of dark volcanic material (see annotations) are still covered by CO₂ frost, even during the Martian spring season, when the scene was imaged. The dark sand often originates from nearby scarps or crater walls, where it is exposed in layers and gradually trickles down onto the Martian surface. Winds then transport and accumulate the dark sand, forming different types of dunes. In the larger dune field, we see a mixture of longitudinal dunes, transverse dunes, and barchanoid ridges, indicating that the winds have blown from different directions.