English: HiRise looked at a small section of Ganges Chasma, which is a trough that makes up part of Valles Marineris. The image is just stunning. Long ago, the surface of Mars in this region was flooded by lava flows. After that, time and wind began changing the surface. Windblown dust and sand covered up everything. If you click on the image and examine the larger version more closely, particularly the region near the edge of this chasm, it looks brighter and smoother than the lava flows underneath. Could this be sediments put in place by flowing water? Or did an explosive v0lcanic event layer the region with fine dust? Or, was it the work of the incessantly blowing Martian winds depositing layer upon layer of fine dust? A combination of all these factors?