From the novelette "The Moon Pool" (1918), by A. Merritt, rated by H.P. Lovecraft the tenth best weird tale of all time:
"And now, Goodwin, for the better understanding of what follows and to guide you, should I -- not be able -- to accompany you when you go there, listen carefully to my description of this place: Nan-Tanach is literally three rectangles. The first rectangle is the sea-wall, built up of monoliths. Gigantic steps lead up from the landing of the sea-gate through the entrance to the courtyard.
"This courtyard is surrounded by another, inner basalt wall.
"Within the courtyard is the second enclosure. Its terrace, of the same basalt as the outer walls, is about twenty feet high. Entrance is gained to it by many breaches which time has made in its stonework. This is the inner court, the heart of Nan-Tanach! There lies the great central vault with which is associated the one name of a living being that has come to us out of the mists of the past. The natives say it was the treasure-house of Chau-te-leur, a mighty king who reigned long 'before their fathers.' As Chau is the ancient Ponapean word both for sun and king, the name means 'place of the sun king.'
"And opposite this place of the sun king is the moon rock that hides the moon pool."
Joshi, among others, notes many common elements between "The Moon Pool" and "Call of Cthulhu": the tilting door to the otherworldly horror, the Pacific island setting, all that basalt, etc. (Ponape shows up not in "Call of Cthulhu" but in "Shadow Over Innsmouth".)
But he doesn't mention the thing that jumped out at me when I read it:
I mean -- doesn't that strike anyone else as an obvious influence?
The Chau-te-leur, by the way, is a real figure, although Wikipedia transliterates him as the Saudeleur and translates it as "lord of the immediate area." Pretty spooky, eh, kids?