Even on earth Denali makes Everest look "small" despite being like 2 miles shorter in terms of sea level, because it's not perched on top of shitloads of other mountains. (base to peak Denali is like 19,000 feet vs everest's 12,000ish)
And then there's the one in Hawaii that's even bigger than that, but its base is on the ocean floor.
But yeah, all 3 of those combined are like... close to as tall as the volcano on mars, and the whole of yellowstone's calderas are about 1/10 as wide lol.
For reference:
http://upload.wikimedia.org/wikipedi...restMosaic.jpg
From the space station.
The 2 big peaks with snow flying off them are Everest (right) and Makalu (left, looks bigger but it's not).
Meanwhile, Olympus Mons is roughly 2.5 times as tall as the highest point there, and roughly 5 times as wide as that entire collage.