“…Long-term aqueous activity on the surface of the planet is indicated by fluvial (e.g., Mars Channel Working Group, 1983;Edgett, 2000a, 2000b) and lacustrine features (e.g., Squyres, 1989;Grin, 1999, 2001); phased degradation of impact craters (e.g., Chapman and Jones, 1977;Craddock and Maxwell, 1993); permafrost (e.g., Lucchitta, 1981); periglacial (e.g., Squyres, 1979) and glacial landforms (e.g., Lucchitta, 1982;Kargel et al, 1995); and outflow channels (e.g., Baker and outflow channels, which either terminate at the boundary (Parker et al, 1993) or fade into the northern plains (Ivanov and Head, 2001), including the prominent circum-Chryse (e.g., Rotto and Tanaka, 1995) and recently identified northwestern slope valleys (NSVs, Dohm et al, 2000Dohm et al, , 2001a outflow channel systems; (3) the relatively low density of superposed impact craters in the northern plains compared to the southern densely cratered highlands (Barlow and Bradley, 1990;Parker et al, 1993), and its extremely flat topography at the distal reaches of the outflow channel systems (Head et al, 1999); (4) the broad occurrence of wide age-ranging glaciers that are interpreted to be linked to magmatic-triggered flooding and associated short-lived (tens of thousands of years) environmental/climatic changes (Baker, 2001;Cabrol et al, 2001aCabrol et al, , 2001bCabrol et al, , 2001c; and (5) the chemical signatures reported for the northern plains, including high abundances of S and Cl or the possible existence of sulphate minerals and chloride salts, making a putative andesite-rich component or weathered basalt the dominant material type in the lowlands (McSween et al, 1999;Zuber, 2001;Wyatt and McSween, 2002). Standing bodies of water, therefore, best explain such evidence, though volcanism , tectonism (Sleep, 1994), eolian modification (Malin and Edgett, 2000a), ground volatile and debris flow activity along the highland-lowland boundary (Tanaka, 1997;…”