At the Mountains of Madness is a novella by horror writer H. P. Lovecraft, written in February/March 1931 and rejected that year by Weird Tales editor Farnsworth Wright on the grounds of its length. It was originally serialized in the February, March, and April 1936 issues of Astounding Stories. It has been reproduced in numerous collections.
The novella’s title is derived from a line in “The Hashish Man,” a short story by fantasy writer Edward Plunkett, Lord Dunsany: “And we came at last to those ivory hills that are named the Mountains of Madness…” (Wikipedia)
The outside world knew, of course, of our program, and was told also of Lake’s strange and dogged insistence on a westward—or rather, northwestward—prospecting trip before our radical shift to the new base. It seems that he had pondered a great deal, and with alarmingly radical daring, over that triangular striated marking in the slate; reading into it certain contradictions in nature and geological period which whetted his curiosity to the utmost, and made him avid to sink more borings and blastings in the west-stretching formation to which the exhumed fragments evidently belonged. He was strangely convinced that the marking was the print of some bulky, unknown, and radically unclassifiable organism of considerably advanced evolution, notwithstanding that the rock which bore it was of so vastly ancient a date—Cambrian if not actually pre-Cambrian—as to preclude the probable existence not only of all highly evolved life, but of any life at all above the unicellular or at most the trilobite stage. These fragments, with their odd marking, must have been five hundred million to a thousand million years old.