High-resolution imaging data sets were used to identify and investigate a discrete stratigraphic unit exposed in the walls of impact craters throughout Chryse and Acidalia Planitiae, Mars. The unique morphology and spectral signatures observed in this unit, which include fine-scale layering, lensing, pinching, and elevated hydration signatures, all indicate that this material was deposited in a suite of aqueous environments. Furthermore, this unit’s widespread distribution and relationship to regional topography suggests an origin from the circum-Chryse outflow channels. While earlier studies have suggested that large quantities of outflow channel effluents are located throughout this region, this analysis is the first to identify and characterize the outcrop-scale morphology and spatial distribution of this extensive unit. These observations imply that the northern plains of Mars served as a global depocenter for immense volumes of water and sediment early in martian history.