Early anthropologists studying the Navajo peoples of the Western United States quickly identified a rich, animalistic pantheon of supernatural beings. Over three hundred specific, detailed descriptions of Navajo heroes, villains, and co-habitants were cataloged, and it was freely admitted that these represented a fraction of the complete ecology. Researchers were assured that these supernatural beings were either: (1) still around, perhaps just beyond the next mesa; (2) gone, but only recently - and perhaps they will return soon; or (3) still here, but in hiding.
The eventual discovery of the Strange Worlds' doors, which at least simulated time travel, presented the opportunity to verify these claims. Alas, no evidence of the Navajo pantheon could be found in the past. But what of elsewhere? Some descriptions were vague and could be applied to just about any flying humanoid or intelligent reptile or (for that matter) many neo-animals. But other descriptions were extremely specific and very closely fit Panzerscorps or Harpies, or dire animals.
Then there were descriptions that matched no known human, alien, or inhabitant of Heinlein's Empire. Could they come from an area of Red not yet explored? There was a certain logic to this. One would expect a connection between the Western Americas in Yellow and the North Atlantis continent in Red. Perhaps the Navajo pantheon dwells there.
Confirmation of this theory must wait until Emperor Heinlein relaxes travel restrictions, or until convenient doors opening into Atlantis are discovered, or both.