gene phillips wrote:

Add to that a 1965 episode, "The Mound Builders," in which Henry Silva plays the survivor of a lost Aztec city who enlists Dan'l's help to find some treasure in hostile Shawnee country. Naturally, one never sees the lost city, but that's a fantasy-trope worth including on the list.

If we're counting lost civilizations, there's a really offbeat episode of Wagon Train ("Princess of a Lost Tribe") that has Robert Horton and others discovering an actual surviving Aztec city, a walled city hidden in the mountains and ruled by Raymond Massey as Montezuma IX.