Fluvial Mapping of Mars (IMAGE) Geological Society of America Caption (A) A suite of ridges on Mars (at -67.64°E, 43.37°S). To determine whether features are ridges or valleys, the researchers rely on lighting in the impact craters (depressions). Based on the craters, the light is coming from the top of the image. Because the fluvial ridges are casting shadows to the south, they can infer that the feature is sticking up from the surface--a ridge rather than a valley. (B) A similar, "analogue" environment on Earth. Fluvial ridges similar to the ones on Mars are in California's Amargosa river system, although with water still running through the system, it's the active precursor to the ridges that are remnant on Mars. Credit Images courtesy J. Dickson. Usage Restrictions Images courtesy J. Dickson. License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.