ANALYSES OF ANCIENT VALLEY NETWORKS AND PALEOLAKE BASINS HAVE PROVIDED IMPRECISE CONSTRAINTS ON THE PEAK ENVIRONMENTAL CONDITIONS OF EARLY MARS. THE CHANNEL-FORMING DISCHARGE FOR MEASURED PALEOCHANNELS INDICATES RUNOFF PRODUCTION ON THE ORDER OF 1 CM/DAY DURING EVENT FLOODS. TO FILL AND OVERFLOW PALEOLAKES CONTRIBUTING WATERSHEDS HAD TO PRODUCE NO MORE THAN 0.1 M/YR OF RUNOFF ASSUMING NO MORE THAN 1 M/YR OF EVAPORATION FROM THE PALEOLAKE. THESE BASELINE REQUIREMENTS SUGGEST AN ARID TO SEMIARID PALEOCLIMATE WITH MODERATE RUNOFF PRODUCTION DURING THE WETTER EPOCH IN EARLY MARTIAN HISTORY. ONGOING STUDIES OF HIGHLAND SURFACES SUGGEST EVEN DRIER CONDITIONS WITH SLOW EROSION OF IMPACT CRATERS DURING MOST OF THE NOACHIAN PERIOD BEFORE THE VALLEY NETWORKS FORMED. THE PROPOSED WORK WILL SIGNIFICANTLY ADVANCE OUR UNDERSTANDING OF RUNOFF PRODUCTION ON MARS BY CHARACTERIZING THE CONTRIBUTING WATERSHEDS FOR VALLEY NETWORKS AT A HIGH LEVEL OF DETAIL. WE WILL TEST THE HYPOTHESIS THAT RUNOFF ORIGINATED FROM RESTRICTED AREAS OF THE LANDSCAPE AND QUANTITATIVELY DETERMINE WHY THIS MAY BE THE CASE. WE HAVE THREE SPECIFIC OBJECTIVES: 1. WATERSHED MAPPING. IN 12 STUDY AREAS THAT SAMPLE A WIDE RANGE OF TOPOGRAPHY IN THE TYRRHENA AND CIMMERIA HIGHLANDS WE WILL MAP ALL RELICT TRIBUTARY VALLEYS AND DELIMIT AREAS THAT DID NOT DEVELOP VALLEYS OR CHANNELS. WE WILL DETERMINE WHETHER HIGH IMAGE RESOLUTION REVEALS DENSER OR MORE EXTENSIVE FLUVIAL NETWORKS THAN PREVIOUS STUDIES HAVE FOUND. 2. EVALUATING INFLUENCES ON FLUVIAL DISSECTION. IN THE DISSECTED AND UNDISSECTED AREAS WE WILL MEASURE CONTRIBUTING AREA RELIEF SLOPE CONCAVITY AND SURFACE INTEGRATION. WE WILL DETERMINE WHICH OF THESE FACTORS HAD A STATISTICALLY SIGNIFICANT INFLUENCE ON TRIBUTARY DEVELOPMENT AND CONSTRAIN THE THRESHOLD TOPOGRAPHIC CONDITIONS FOR FLUVIAL INCISION DURING THE WETTER EPOCH IN EARLY MARTIAN HISTORY. AS PART OF THIS OBJECTIVE WE WILL TEST WHETHER THE RESULTS ACCURATELY PREDICT THE DISTRIBUTION OF FLUVIAL VALLEYS IN OTHER WATERSHEDS WITHIN TYRRHENA TERRA AND TERRA CIMMERIA. 3. REFINEMENT OF HYDROLOGIC RELATIONSHIPS. WE WILL APPLY THE RESULTS FROM OBJECTIVES 1 AND 2 TO BETTER CONSTRAIN THE EFFICIENCY OF RUNOFF PRODUCTION AND THE MINIMUM RATES OF RAINFALL OR SNOWMELT IN VALLEY NETWORKS WITH RECOGNIZED PALEOCHANNELS. BY DIFFERENTIATING THE CONTRIBUTING AND NON-CONTRIBUTING SURFACES AND RECOGNIZING WHICH TOPOGRAPHIC SURFACES PRODUCED VALLEYS MOST EFFICIENTLY WE WILL SUBSTANTIALLY IMPROVE OUR UNDERSTANDING OF THE RELATIONSHIP BETWEEN DISCHARGE AND CONTRIBUTING AREA. THIS PROJECT WILL ENHANCE THE SCIENTIFIC RETURN OF MARS MISSION DATASETS INCLUDING THE MARS RECONNAISSANCE ORBITER CONTEXT CAMERA MARS ODYSSEY THERMAL EMISSION IMAGING SYSTEM AND MARS GLOBAL SURVEYOR MARS ORBITER LASER ALTIMETER SATISFYING THE MAIN OBJECTIVE OF MDAP. NO FIELD WORK THEORETICAL MODELING OR STUDIES OF OTHER PLANETS ARE PROPOSED.