Quote Originally Posted by jwbjerk
I would also expect very little precipitation, or accumulation of ice and snow on the top (except perhaps in more or less permanent shadow). Evaporation happens more readily as air pressure decreases. Snow and Ice may also "sublimate", i.e. go directly from solid to gas.
You're right about sublimation and evaporation. I only need these things to be high enough so that they're mainly bare rock, there is hardly any erosion (so that they can be essentially lunar terrain, scarred with billions of years of craters) and the air is effectively vacuum.

The glaciers should ideally go up most of the way to the top of the mesa... Imagine the Andes mountains, rising from a coastal plain, except as you go further inland the mountains keep getting higher and higher, the air thinner and thinner, until the glaciers fall away, and as you climb the last thousand meters (with breathing and pressure gear) the terrain flattens out until you are on a giant cratered plateau. I only need the plateau to be high enough that whatever glaciers there are have petered out, high enough that sublimation keeps the rock clear at the top. I chose 25000 meters because the 1/32 figure seemed close enough to vacuum, but maybe I only need 1/4 or 1/8 of sea level pressure to achieve this effect.