Today's Image of Mars shows a closeup of the eastern wall of a pit in Amazonis Planitia, courtesy of HiRISE. The darker streaks you see are the result of dust avalanches that removed a thin layer of light dust that covers the rest of the surface.
You can see in the upper part of this pit near the rim that there are four distinct layers, which is indicative of at least four separate lava flows that covered the area. The terrain directly surrounding the pit is much less defined, which may be the result of a heavy dust covering that has muted the features.
Another sign that there is a havy dust covering surrounding the pit is the bluish haze just around the rim, which the HiRISE team believes could be suspended dust. This can happen if wind lifts some of the dust covering into the air.
Clicking on this image will take you to the original high resolution image from HiRISE. [See their caption on images of this pit]