Tuesday, April 17, 2012, 4:21 PM Valles Marineris The magnificent Valles Marineris valley system is comprised of a multitude of valleys and canyons stretching 3,000 miles, from the Tharsis Planitia at the western end of the canyon system to the Elysium Planitia at the east end. The region is filled with extinct volcanos and other peculiar geological findings. The atmosphere is almost 80 percent carbon dioxide here, rising to well over 95% further east and making it hazardous for those who need to breath oxygen. Slugfest keeps sawing! "All rocks off yet? No can tell!"