Dark Patches Formed by Craters

n the ancient past, this area of Mars was bombarded by impactors, forming craters of various sizes in the light-toned material. Some time after that, a darker material blanketed and covered the field, filling in the craters. Eventually, that blanketed material itself became rock. Long after that, erosive forces (likely wind) acted in this area removing both dark and light-toned material, like an archeologist using a brush to reveal buried structures.