River deposits on Mars. Satellite image of a sinuous ridge on the alluvial deposits of a bajada in the Orson Welles crater, on the surface of Mars. Alluvial fans are piles of debris deposited by rivers when they emerge from the mountains and enter a mostly dry valley. A bajada consists of a series of coalescing alluvial fans along a mountain front. On the surface of this bajada are many sinuous ridges that mark the path that streams of water took as they flowed into the crater. Imaged by the High Resolution Imaging Science Experiment (HiRISE) camera on NASA's Mars Reconnaissance Orbiter (MRO) satellite.