Some areas in the Elysium quadrangle are geological young and have surfaces that are hard to explain. Some have called them Platy-Ridged-Polygonized terrain. The surface has been suggested to be from pack ice, basalt lava, or a muddy flow. Using HiRISE images the heights of the ridges of the surface were measured. Most were less than 2 meters. This is far smaller than what is expected from lava flows. The high resolution photos demonstrated that the material seemed to flow which would not occur with pack ice. So, the researchers concluded that muddy flows cover the surface.