Outflow channels and valley systems are evidence of water flow on the surface of Mars. Whenever there is a consequent flow of water on an irregular surface, temporary impoundment in surface depressions will form lakes. A classification of martian lake basins based on the location of the basin in respect to water sources is proposed. The classes are Type 1: Valley-head basins, Type 2: Intravalley basins, Type 3: Valley-terminal basins, and Type 4: Isolated basins. Martian lakes are ephemeral features. Many craters and irregular depressions impounded water only until the basins filled and overflowed. Water escaping by spillover rapidly cut crevasses in the downstream side of basins and drained the ponds. Clastic lacustrine sediments collected in the lakes as flowing water lost velocity and turbulence. Evaporitic deposits may be significant in those basins that were not rapidly drained. Sediments deposited in lake basins form smooth, featureless plains. Lacustrine plains are potentially candidate sites for Mars landings and for the search for evidence of ancient life.

Mars displays a variety of volcanic materials from high standing constructs to smooth plains. These materials are evaluated in terms of their susceptibility to thickness determination, and a representative area is analyzed. The Martian ridged plains are much like lunar maria in both surface expression and apparent mode of emplacement. Flooded craters within the ridged plains materials provide an estimate of the thickness distribution. In the Tharsis region, ridged plains materials occur as part of the layered sequence on the east flank of the Tharsis dome. Partially buried craters indicate that the ridged plains materials range from zero meters thick at their eastern limit to over 1.5 km thick westward on the flank of the dome where they are overlain by younger materials. These materials are responsible for only a small portion of the total relief of the Tharsis dome.

The 1600‐km‐long Maja Valles outflow system of Mars consists of three major divisions including the upper valley on Lunae Planum, the canyon section across Xanthe Terra, and the lower valley across western Chryse Planitia. Although water released from the source in Juventae Chasma could reach the terminus of the present day valley system within 40 hours, the original outflow did not traverse the Martian surface as an uninterrupted flow, nor was the source basin emptied instantaneously. The initial flood ponded on northern Lunae Planum and near the western edge of Chryse Planitia, significantly prolonging the lifetime of surface flow. Calculation of pond volumes and maximum discharge rates through various parts of the channel system, assuming full‐bank discharge, allows an estimate of minimum duration of water flow through the outflow complex. About four (terrestrial) months are required to empty Juventae Chasma, and another 10 months are required to drain the impoundment on Lunae Planum. Thus, the history of erosion and sedimentation in the lower reaches of the drainage system is potentially much more complex than that of outflow from the source region.

Abstract. The Marsokhod rover returned data from six stations that were used to decipher the geomorphology and geology of a region not previously visited by members of the geomorphology field team. Satellite images and simulated descent images provided information about the regional setting. The landing zone was on an alluvial apron flanking a mountain block to the west and a playa surface to the east. Rover color images, infrared spectra analysis of the mountains, and the apron surface provided insight into the rock composition of the nearby mountains. From the return data the geomorphology team interpreted the region to consist of compressionally deformed, ancient marine sediments and igneous rocks exposed by more recent extensional tectonics. Unconsolidated alluvial materials blanket the lower flanks of the mountains. An ancient shoreline cut into alluvial material marks a high stand of water during a past, wetter climate period. Playa sediments floor a present-day, seasonally, dry lake. Observations made by the rover using panoramic and close-up (hand specimens--scale) image data and color scene data confirmed the presence of boulders, cobbles, and fines of various provinces. Rover traverses to sites identified as geologically distinct, such as fan, channel, shoreline, and playa, provided useful clues to the geologic interpretations. Analysis of local rocks was given context only through comparison with distant geologic features. These results demonstrated the importance of a multifaceted approach to site interpretation through comparison of interpretations derived by differing geologic techniques.

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