General geology and geomorphology of the Mars Pathfinder landing site

The Mars Pathfinder (MPF) spacecraft landed on relatively young (late Hespe rianearly Amazonian; 3.1-0.7 Ga) plains in Chryse Planitia near the mouth o f Ares Vallis. Images returned from the spacecraft reveal a complex landsca pe of ridges and troughs, large hills and crater rims, rocks and boulders o f various sizes and shapes, and surficial deposits, indicating a complex, m ultistage geologic history of the landing site. After the deposition of one or more bedrock units, depositional and erosional fluvial processes shaped much of the present landscape. Multiple erosional events are inferred on t he basis of observations of numerous channels, different orientations of ma ny streamlined tails from their associated knobs and hills, and superpositi on of lineations and streamlines. Medium- and small-scale features, interpr eted to be related to late-stage drainage of floodwaters, are recognized in several areas at the landing site. Streamlined knobs and hills seen in Vik ing orbiter images support this inference, as they seem to be complex forms , partly erosional and partly depositional, and may also indicate a series of scouring and depositional events that, in some cases, further eroded or partially buried these landforms. Although features such as these are cited as evidence for catastrophic flooding at Ares Vallis, some of these featur es may also be ascribed to alternative primary or secondary depositional pr ocesses, such as glacial or mass-wasting processes. Close inspection of the landing site reveals rocks that are interpreted to be volcanic in origin a nd others that may be conglomeratic. If such sedimentary rocks are confirme d, fluvial processes have had a greater significance on Mars than previousl y thought. For the last several hundred million to few billion years, eolia n processes have been dominant. Dunes and dune-like features, ventifacts, a nd deflation and exhumation features around several rocks probably are the most recent landforms. The relatively pristine nature of the overall landsc ape at the MPF site suggests weathering and erosion processes on Mars are e xceptionally slow.