Ripoff of The Blob?
I notice The Blob was about a year earlier and has a similar monster.
I say "ripoff" because it seems like it may copy The Blob to some extent, but actually I think the premise of Caltiki may be scarier. There is something vaguely creepy about Mayan art, so it's not surprising someone decided to make a scary movie about the Maya. The narration at the beginning gives the film a very scary setup.
Actually it's mostly fictional. We've discovered that the Maya didn't really flee from their area. They still live in the same areas. The fall of the classic cities in the 9th century was mostly a fall of the political elite. It apparently wasn't considered that big a deal by the common people.
I also think it's kind of funny that the narrator says no one has been able to figure out why the Maya fled, yet there is a volcano erupting at the beginning. Wouldn't you think it might have something to do with this volcano? But in reality there are no volcanoes close to the Maya classic cities. It does help to make the beginning scary, though.
"Extremism in the pursuit of moderation is no vice."