The western Utopia Planitia in the Northern mid-latitudes of Mars is marked by a peculiar type of depression with scalloped edges and by a network of polygonal fractures.
The scalloped depressions are typical features; a smooth layered terrain located between 40 and 60 degrees in both hemispheres. Scalloped depressions probably form by removal of ice-rich subsurface material by sublimation (ice transforming directly from a solid to a gaseous state), a process that may still be active today. Isolated scalloped depressions generally… [More at link]