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During the Mariner 9 extended mission the recession of the north polar ice cap was monitored for 130 days. The edge of the cap displayed a peculiar polygonal outline during most of this period. Regional topographic control is suggested as the most likely cause of the polygonality. Whereas densely cratered terrain dominates the south polar region, moderately cratered plains underlie the polar deposits in the north polar region. The mottled cratered plains have been mantled by light deposits located in annular rings south of 70°N. The erosional boundaries between these deposits and the subjacent cratered plains are gradational, show no local topographic relief, and display a spiral serrated circumpolar pattern suggesting eolian erosion. Smooth plains and ‘etch-pitted’ plains underlie the central polar layered deposits in both polar regions. In addition, these plains have one other morphological variant in the north. Here they display a pattern of very coherent ripplelike wave forms varying in wavelength from several hundred meters to a few kilometers. The central polar layered deposits (laminated terrain) that underlie the permanent ice caps display the same depositional and erosional characteristics, age relationships, and areal distributions in both polar regions. Although the upper surfaces of the two deposits are at about the same pressure altitude, the northern deposits are apparently substantially thicker.