Drainage morphometry and geologic mapping place new constraints on valley origin in Margaritifer Sinus, Mars. Preserved valleys are constant width, typically head near divides, possess fourth-order trunk segments, and were formed from late Noachian into earliest Hesperian time. Relative to terrestrial systems, the Martian valleys have low densities (<0.1 km/km2), relief ratios (0.001–0.13), and ruggedness numbers (0.005–0.086), and the sediment volume in associated sinks exceeds the volume excavated by upstream segments. Valley characteristics are consistent with formation by precipitation-recharged ground-water sapping within a layered, permeable substrate.

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