MARS VALLEY NETWORKS ARE AMONG THE BEST LINES OF EVIDENCE FOR WIDESPREAD FLUVIAL MODIFICATION OF THE PLANET S SURFACE BUT THE CLIMATIC CONDITIONS PRESENT DURING THEIR FORMATION REMAIN CONTROVERSIAL. RESEARCHERS HAVE COMPILED GLOBAL MAPS OF VALLEY NETWORKS FROM VIKING AND THEMIS DATA TO ESTIMATE VARIOUS PROPERTIES OF MARS GEOLOGIC HISTORY INCLUDING CLIMATIC CONDITIONS FORMATION TIMESCALES AND EROSION RATES. THE CHANNELS MAPPED BY HYNEK ET AL. (2010) ARE NOW COVERED 96% BY CTX IMAGERY AND 51% BY HRSC DEMS. WE PROPOSE TO USE THESE HIGH RESOLUTION DATA TO CONDUCT DETAILED GEOMORPHOLOGIC STUDIES AND LANDFORM EVOLUTION MODELING AT EIGHT VALLEY NETWORKS SPANNING A WIDE RANGE OF GEOLOGIC SETTINGS TO ADDRESS SEVERAL OUTSTANDING QUESTIONS. SPECIFICALLY WE PROPOSE TWO RELATED TASKS: (1) DETAILED GEOMORPHOLOGIC MAPPING STUDY USING MOLA HRSC CTX AND HIRISE (WHERE AVAILABLE) IMAGERY TO STUDY PALEOFLOW PROPERTIES FORMATIVE PROCESSES. (2) USE THE MARSSIM LANDFORM EVOLUTION MODEL TO EXPLORE SEDIMENTARY HYDROLOGIC AND CLIMATIC CONDITIONS NECESSARY FOR THE OBSERVED DISTRIBUTION AND VARYING DENSITIES OF VALLEY NETWORKS. INTEGRATING ORBITER DATA WITH THE MARSSIM LANDFORM EVOLUTION MODELING HAS PROVEN TO BE AN EFFECTIVE TOOL AT DECIPHERING A PLANETARY SURFACE S GEOLOGIC HISTORY. CHARACTERIZING THE HISTORY OF MARS SURFICIAL WATER AND PALEOCLIMATE REMAIN TOP NASA SCIENCE THEMES AS STATED IN THE 2013-2022 DECADAL SURVEY. WE WILL DIRECTLY ADDRESS BOTH OF THESE THEMES BY USING DATA FROM THE MARS RECONNAISSANCE ORBITER AND MARS EXPRESS TO UNDERSTAND THE HYDROLOGIC PROPERTIES AND FORMATIVE CONDITIONS NECESSARY FOR VALLEY NETWORK FORMATION WHICH WILL YIELD INSIGHTS INTO MARS' PAST POTENTIAL HABITABILITY.