This image shows part of a new geologic map of the Terra Tyrrhena region of Mars that is being prepared by Scott Mest (University of Pittsburgh) and PSI's David Crown for publication as a U.S. Geological Survey Geologic Investigations Series Map. The different colors shown on the map represent different geologic units identified on the Martian surface through analyses of spacecraft images from the Viking and Mars Global Surveyor missions. The map depicts an ancient Martian surface exhibiting numerous impact craters and fluvial valleys, some of which form an extensive, integrated drainage network. The region shown (19.7-23.5°S, 271-273.9°W) is ~300 km across. Click on the map to view a larger version, along with a photomosaic of Viking Orbiter images (from USGS Mars Transverse Mercator quadrangles -20272 and -25272) of the same area shown in the map.