The first expedition of Richard Evelyn Byrd took place in 1928-1930, the period just before the novella was written, and Lovecraft mentioned the explorer repeatedly in his letters, remarking at one point on "geologists of the Byrd expedition having found many fossils indicating a tropical past".
Lin Carter has suggested that one inspiration for At the Mountains of Madness was Lovecraft's own hypersensitivity to cold, as evidenced by an incident where the writer "collapsed in the street and was carried unconscious into a drug store" because the temperature dropped from 60 degrees to 30 degrees Fahrenheit (15 degrees to -1 degree Celsius). "The loathing and horror that extreme cold evoked in him was carried over into his writing," Carter wrote, "and the pages of Madness convey the blighting, blasting, stifling sensation caused by sub-zero temperatures in a way that even Poe could not suggest."
Lovecraft's most obvious literary source for At the Mountains of Madness is Edgar Allan Poe's lone novel, The Narrative of Arthur Gordon Pym, whose concluding section is set in Antarctica. Lovecraft twice cites Poe's "disturbing and enigmatical" story in his text, and explicitly borrows the mysterious phrase "Tekeli-li" from Poe's work. In a letter to August Derleth, Lovecraft wrote that he was trying to achieve with his ending an effect similar to what Poe accomplished in Pym.]
Another proposed inspiration for At the Mountains of Madness is Edgar Rice Burroughs' At the Earth's Core (1914), a novel that posits a highly intelligent reptilian race, the Mahar, living in a hollow earth. "Consider the similarity of Burroughs' Mahar to Lovecraft's Old Ones, both of whom are presented sympathetically despite their ill-treatment of man," writes critic William Fulwiler. "[B]oth are winged, web-footed, dominant races; both are scientific scholarly races with a talent for genetics, engineering, and architecture; and both races use men as cattle." Both stories, Fulwiler points out, involve radical new drilling techniques; in both stories, humans are vivisected by nonhuman scientists. Burroughs' Mahar even employ a species of servants known as Sagoths, possibly the source of Lovecraft's shoggoths.
Other possible sources include A. Merritt's "The People of the Pit", whose description of an underground city in the Yukon bears some resemblance to that of Lovecraft's Elder Things, and Katharine Metcalf Roof's "A Million Years After", a story about dinosaurs hatching from eggs millions of years old that appeared in the November 1930 edition Weird Tales. In a letter to Frank Belknap Long, Lovecraft declared the story to be a "rotten", "cheap", and "puerile" version of an idea he had come up with years earlier, and Joshi suggests it may have provoked him to write his own tale of "the awakening of entities from the dim reaches of earth's history."
The long scope of history recounted in the story may have been inspired by Oswald Spengler's The Decline of the West. Some details of the story may have been taken from M. P. Shiel's 1901 novel of Arctic exploration, The Purple Cloud, which was republished in 1930.
Lovecraft's own "The Nameless City" (1921), which also deals with the exploration of an ancient underground city apparently abandoned by its nonhuman builders, is a clear precedent for At the Mountains of Madness. In both stories, the explorers use the nonhumans' artwork to deduce the history of their species.
On-line text –
Lovecraft on Englishtips:
The Call of Cthulhu
Dragon and Alchemist