Doing a quick google search for Marina Dorotea DeVargas, I don't come up with any hits, so unlike something like Ripley's Believe it or Not, I'll assume this is pure fiction.
Some great Kirby historically-based art. I wonder if Jack had to consult any photo reference for the period costumes and Central American imagery, or did he just wing it? I'd suspect early in his career, Jack probably spent a lot of time in a local NYC library copying historical images when it was called for, or I suppose there may have been a swipe file handy that had various magazine photos of period costumes and the like, but I suspect in this case, Jack did a little research to get the design of the Aztec Pyramid and the Central American face on the stone wall.
Here's the final panel. Nothing is resolved storywise. But I guess there isn't a whole lot you can pack into a 2-pager, plus maybe leaving the tale open-ended appeals to some readers who like to contemplate unsolved mysteries.
