Cyonia Mensae is an albedo feature (region) on Mars. It lies in the planet's northern hemisphere in a transitional zone between the heavily cratered regions to the South, and relatively smooth plains to the North. Some planetologists believe that the northern plains may once have been ocean beds and that Cydonia may have been a coastal zone (though this is still uncertain). Cydonia is covered in numerous mesas, some of which have attracted both scientific and popular attention.