When the tilt begins to return to lower values, the ice sublimates (turns directly to a gas) and leaves behind a lag of dust. The lag deposit caps the underlying material so with each cycle of high tilt levels, some ice-rich mantle remains behind. Note, that the smooth surface mantle layer probably represents only relative recent material. Brain terrain Brain terrain is a region of maze-like ridges 3–5 meters high. Some ridges may consist of an ice core, so they may be sources of water for future colonists. Glaciers See also Deuteronilus Mensae Geology of Mars Glacier Glaciers on Mars Martian dichotomy Nilosyrtis Mensae References Ismenius Lacus quadrangle Mensae on Mars