Where Are the Mountains of Madness?

In Antarctica, in the interior, and the account itself gives the figures. The range was first sighted from the air by Lake's sub-expedition at a probable 76°15′ South, 113°10′ East, and the Elder Things' City lies beyond it. The Field Survey draws that point with its coordinates-on-record mark, which is the firmest mark on the chart.

The expedition's positions

The Miskatonic University Antarctic Expedition of 1930–31 kept a southern base above the glacier at 86°7′ South, 174°23′ East, at a height of about 8,500 feet. The two points lie roughly 850 miles apart. The Survey marks both. The flight that Dyer and Danforth made across the range came after Lake's camp fell silent.

Why the city is filed UNCHARTED

A coordinate is not the same as a route. The account describes the range as higher than the Himalayas, avoided by every expedition since, and the city beyond it as a dead metropolis of stone towers older than any life on land. The Archive stamps it UNCHARTED: its position is on file, but no survey has reached it since, and the leader's own report recommends that nobody try.

That recommendation is the reason the account was written at all: the witness set it down to dissuade a second expedition from sailing.

The interactive map has an Antarctica preset, with coastline, ice shelves and the Survey's detail layer switched on at the right zoom.