“The Mound” is a novella Lovecraft ghost-wrote for Zealia Bishop from late 1929 into early 1930, working from her premise. A Native American mound in Oklahoma conceals a gateway to an underworld, and by day a headless ghost keeps the spot. The narrator, an ethnologist, digs a metal cylinder from the mound; inside is a scroll left by Pánfilo de Zamacona, a Spanish explorer who came from Mexico around 1541.
The realm Zamacona descends into, K’n-yan, is a vast underground kingdom where a telepathic, deathless race worships Cthulhu, Yig, Shub-Niggurath and Tsathoggua. They reshape their bodies at will, materialize and dematerialize, and have degenerated from a once-greater civilization. Captured and mutilated, Zamacona ends as a headless guardian that goes on existing without a head. That image — existence continuing with neither self nor head — sits alongside At the Mountains of Madness and The Shadow Out of Time as one of the three works in which Lovecraft renders a non-human culture in full.