Popular Science, April 1931: The story of Captain William F. Long, adventurer, who weaves a tale of parachuting in search of hidden gold and gems in a living city of the Maya. It's a tale of racist notions of natives bowing to white gods, jungle battles, and un-named Mexican archaeologists with stone idols.
Go ahead and read, if you can stand the excitement
I have no idea how much if any of it is even remotely true (obviously, much of it is problematic, but I don't even know if there ever was a plane flight or a skydive, never mind any of the details). What I do know is that in the wake of several highly publicized legitimate air surveys of Maya ruins, including one by hero pilot Charles Lindbergh (we're still before the rise of Nazi Germany and Lindbergh's political steps), it looks like the press was all too eager to print tales of such derring-do. The New York Times ran Long's story, as they did several other sensationalistic tales of archaeological adventure. Around the same time they started running stories on Mitchell-Hedges, who would eventually produce the Crystal Skull "of Lubantuun."
Spielberg and Lucas said they based Indiana Jones off of the pulp serials of the 1930s and 1940s. I wonder if they knew how close they were to the respectable headlines of the day.