Aram Chaos lies within a 280 kilometer-diameter ancient impact crater in the Southern Highlands of Mars. Uplifted blocks of light-toned layers, composed largely of the iron-oxide hematite and water-altered silicates, indicate that this crater once held a lake.
Scientists suggest that these enormous flood channels were carved quickly within just weeks or months by catastrophic outflows of groundwater over 2.5 billion years ago from beneath Aram Chaos and nearby regions. Today dark (basaltic) dunes fill most of the low regions and the etched areas of the uplifted blocks obscure much of the original crater floor… [More at link]