|MC-09 Tharsis (extending slightly into MC-08 Amazonis)
|19° N, 134° W
|Diameter 625km; height 21km*
|The largest mountain or volcano known on any planet, the wide base of Olympus Mons covers an area comparable to the country of Poland on Earth. This is a shield volcano, now extinct, that rises from the surrounding lowlands to form a domed shape with a complex multiple caldera at its summit.
* Heights of mountains on Mars are measured from the datum, the Martian equivalent of 'sea level' on Earth. The nature of the geography around Olympus Mons means that it actually rises somewhat higher above its surrounding plains than from the datum point. From base to peak, the physical height of the volcano is actually 26km, rather than the formal 21km measured from the datum.