The plains around the larger volcanoes have numerous flow features and are almost certainly volcanic. Other plains have ridges and rille-like features that resemble those on the Moon and so are suspected of being volcanic like the lunar maria. Where visible in section, the plains are layered, perhaps indicating interbedded materials of different origins. This volcano, the largest on Mars, measures over 600 km across at the base, and is about 27 km high. It is surrounded by a well-defined scarp that is up to 6 km high.
Flows drape over the scarp and extend onto tile surrounding plains.
Parts of the plains surrounding tile volcano are characterized by ridged and grooved terrain that is faulted in places. The origin of this terrain is not known. The stereogram permits a greater appreciation of the structure of Olympus Mons, especially the caldera and the scarp. Summit Caldera of Olympus Mons . This mosaic consists of several frames that show features on the surface as small as 18 meters across.