US GEOLOGICAL SURVEY / SCIENCE PHOTO LIBRARY US GEOLOGICAL SURVEY / SCIENCE PHOTO LIBRARY
This mosaic of Viking Orbiter photos shows the boundary scarp between Mars' ancient cratered highlands and the northern plains to the east of Mangalla Valles. Ancient river channels run north through the cratered highlands, but are covered north of the scarp by young lava flows. The large impact crater just north of the scarp shows flow- like ejecta lobes, which may form due to the presence of subsurface water or ice.
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