The Mars Pathfinder landing site (MPLS) was selected for its location at the mouths of Ares and Tiu Valles outflow channels on Mars, where sediments from a variety of geologic units could have accumulated in a lacustrine environment. Recent geologic mapping at 1:2M scale of the Xanthe Terra channels and Chryse Planitia near MPLS reveals a progression of fluvial erosion and deposition throughout the Hesperian period. From the geology, the watersheds of the channels were inferred, and a sequence of paleogeologic maps was produced. Three outflow episodes are recognized: (1) broad sheetwash during the early Hesperian, emanating from eastern Valles Marineris and equatorial chaos regions, with initial erosion into highland plateau basement, (2) early channel formation, and (3) subsequent flooding which deepened the channels to their current morphologies. The most recent flooding issued from Simud and Tiu Valles during the late Hesperian, indicated by stratigraphic superposition, striations along the floor of the channel, and the orientation of streamlined islands in the flood direction. This suggests that surface sediments deposited at MPLS are most likely to have come from these channels, and to a lesser extent from Ares Vallis. A ranking scheme was developed to assess the potential origins for the sediments found at MPLS. The most abundant materials are inferred to have come from the Noachian and Hesperian highland plains and reworked sediments from previous floods. Underlying materials from earlier floods could also be found at MPLS as ejecta from nearby impact craters. ¿ 1999 American Geophysical Union