"Honduras, December 1920" was an unproduced episode of The Young Indiana Jones Chronicles, which would have been part of the third season of the series. The subject of the episode was to have been archaeology with a follow-up intended with the also unrealized "Brazil, December 1921".
While on a field trip with Herbert Spinden, after they arrive at a Honduran port and meet some Banana Republic types before they begin, Indy would for the first time (chronologically) encounter René Emile Belloq, his future rival, who initially has a friendly relationship with him. The story was to depict their discovery of a crystal skull in the ruins of a Mayan city where Jones and Belloq would have tried to decipher Mayan hieroglyphs at the ball court, as well as discussing possible sacrifices and rituals. However, Belloq steals the skull and sells it to the adventurer Mitchell-Hedges.
It's possible that this episode would have explained the event as referenced by Chattar Lal in Indiana Jones and the Temple of Doom that saw Indy accused of being a grave robber instead of an archaeologist while on an adventure in Honduras. This has since been attributed to events surrounding the Crystal Skull of Cozan in the opening chapter of the Indiana Jones and the Philosopher's Stone novel.
The crystal skulls have been incorporated into multiple Indiana Jones stories over the years since. Philosopher's Stone novelist Max McCoy featured the Cozan skull as a subplot which ran throughout his Indiana Jones books, including an encounter between Jones and Belloq in his 1996 novel Indiana Jones and the Dinosaur Eggs. Lucas himself eventually dealt with the skulls in 2008 film Indiana Jones and the Kingdom of the Crystal Skull which included Indiana Jones explicitly pointing out that the Crystal Skull of Akator was not the Mitchell-Hedges Skull.