High Quality Content by WIKIPEDIA articles! Scalloped topography is common in the mid-latitudes of Mars, between 45° and 60° north and south. It is particularly prominent in the region of Utopia Planitia, , in the northern hemisphere, and in the region of Peneus and Amphitrites Patera in the southern hemisphere. Such topography consists of shallow, rimless depressions with scalloped edges, commonly referred to as "scalloped depressions" or simply "scallops". Scalloped depressions can be isolated or clustered and sometimes seem to coalesce. A typical scalloped depression displays a gentle equator-facing slope and a steeper pole-facing scarp. This topographic asymmetry is probably due to differences in insolation. Scalloped depressions are believed to form from the removal of subsurface material, possibly interstitial ice, by sublimation (direct transition of a material from the solid to the gas phase with no intermediate liquid stage). This process may still be happening at present. In Utopia Planitia, a series of curvilinear ridges parallel to the scarp are etched on the floor of large scalloped depressions, possibly representing different stages of scarp erosion. Sometimes the surface around scalloped terrain or scalloped topography displays "patterned ground", characterized by a regular pattern of polygonal fractures. These patterns indicate that the surface has undergone stress, perhaps caused by subsidence, desiccation, or thermal contraction. Such patterns are common in periglacial areas on Earth. Scalloped terrains in Utopia Planitia display polygonal features of different sizes: small (abut 5–10 m across) on the scarp, and larger (30–50 m across) on the surrounding terrains. These scale differences may indicate local difference in ground ice concentrations.