English: Nanedi Valles, a roughly 800-kilometre valley extending southwest-northeast and lying in the region of Xanthe Terra, southwest of Chryse Planitia. In this view, Nanedi Valles ranges from approximately 0.8- to 5.0-kilometre wide and extends to a maximum of about 500 metres below the surrounding plains. This valley is relatively flat-floored and steep-sloped, and exhibits meanders and a merging of two branches in the north. The valley's origins remain unclear, with scientists debating whether erosion caused by ground-water outflow, flow of liquid beneath an ice cover or collapse of the surface in association with liquid flow is responsible. Image captured by the High-Resolution Stereo Camera (HRSC) onboard ESA's Mars Express on 3 October 2004 during orbit 905. North is to the right.