I'm trying to find a short story about Martians being found living on the peak of Mount Everest. The story precedes the first climb of Everest (1953) and had the protagonist reach the summit in a helicopter or plane, rather than by climbing. I read it in an anthology of short stories sometime in the 80s. The Martians were there because the low atmospheric pressure and cold temperatures mimicked Martian conditions, but I don't recall if they had a mission to complete.
This is Everest by Isaac Asimov.
The story concerns a mountain climber named James Abram Robbons who is the first man to reach the summit of Mount Everest, after having been dropped there by airplane. Robbons is picked up again two weeks later, and he reports that the summit of Everest is the location of a Martian outpost, and that the yeti are actually Martians.