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The Mare Boreum geologic map portrays the north polar area of Mars above lat 65˚ N. The area contains five physiographic provinces: (1) a residual ice cap characterized by troughs with a counterclockwise outward spiral pattern (Mariner 9 frames DAS 13317550 and DAS 13353320); (2) layered terrain adjacent to the ice cap, exposed within the spiral troughs; (3) a circumpolar band of low...