White's site primarily focuses on history/realism. not the fantastic. (I mean, besides the very premise of the site.) However, whenever we think of medieval times, we're less inclined to think of the real figures and politics, and more of the fairy tale version of it. With the possible exception of (A very broadly conflated version of) the ancient Middle East no region/era has been more associated with magic over real history than Medieval Europe. Perhaps this may be the result of J.R.R. Tolkien, whom most fantasy fiction draws from, placing his universe in a Medieval European setting. It may have been Walt Disney. But ultimately, this creates the temptation to ponder what the fantasy version of Medieval America is like, either when extrapolating what myth and folklore exists, or wanting to set some kind of role playing campaign in it. As I've said, White doesn't get into this much--he seems to primarily want to focus on the somewhat real. Plus, it's very easy to get taken over by popular culture, which I'll get to later.
He does delve a little into what imaginary beasts people might come up with. Almost hidden on the Herdsmen page is a link to the Jackelope, an imaginary animal that is a rabbit with antlers. Looking in the archives, you see four more monsters have been cooked up. From the Appalachians, you have Mothman. From the mid-Atlantic, the Jersey Devil. From the Southwest, you have a Roswell Alien. And of course, from the Northwest, Bigfoot. These are essentially cryptids; Creatures that have not been proven to exist, but have attracted sightings and claims that they're very real.
1) That we came from a society that simply does not believe in elves or goblins, and it's hard to go back. With the exception of the Jackelope, many people do believe in these creatures, or at least more than other fantastic creatures. So it could be something like "Unicorns are ridiculous, but Jersey Devils, that's something to be afraid of!"
2) Regional issues. A lot of mythical creatures that are in the popular lexicon like elves and trolls simply come from across the sea. So it may have been White's intention to focus on the creatures that emerged from American folklore.
3) Public domain. Would we believe in things like Wookies and Predators in the future? Perhaps, but that might cause legal problems. I would have also guessed at first that White wanted to steer clear of things with Industrial Age connotations except for the Alien-like being ruled that out.
So here we are, ready to flesh out what folk beliefs in legends exist in Medieval America. I suppose we could divide it all into three categories. Public domain, modern characters, and real world figures.
The first part would be the folklore figures. As mentioned, we got into the strange cryptid things. Some of the creatures from American folklore and urban legends include the Goatman, the Hodag and the Squonk. It's also possible Native American myths like the Wendigo, and the Thunderbird persist. And finally, much of the Caribbean folklore (Which would be brought along with Voodoo) would make its way to the gulf. It's too extensive to get in there too. And then there are the heroes. Paul Bunyan, Pecos Bill, John Henry, Zorro, and the like may catch on.
Some of the people featured in tall tales are actually real, like Calamity Jane. Daniel Boone, Davey Crockett and countless others have gained folk hero status, and could probably survive, especially in Texas and the mountain states. Paul Revere might remain an important hero in the Northeast. Many presidents and founding fathers could conceivably play a big role, but there might be too many records of them to truly retain "folk" status. I imagine the major presidents like Washington and Lincoln will still remain known, however. Sports heroes may also become mythic figures, although mostly the ones who truly symbolized their field like Wayne Gretsky and Michael Jordan. Granted, many athletes tend not to stand the test of time, but in America we've really hyped the people up. Will the centuries turn them into warriors? Give them magic powers?
Movie stars would be an interesting case. I've pointed out California would likely canonize Hollywood figures. Probably not a lot of actors would be famous as historical or folk characters. Maybe a few who were personified as a certain type like Clint Eastwood. Likely a few tragic ones like Marilyn Monroe. And maybe any that went on to be high profile historical leaders like Arnold Schwarzenegger. Musicians might sift more in the tides of time, except those with a cult of personality all their own. White had an image of Elvis on his site, so it's very possible he would work himself into the folklore of this age.
Literary characters like Tom Sawyer and the headless Horsemen might exist as legends. I think the fictional work with the biggest penetration would possibly be the Wizard of Oz. The Wicked Witch, the Yellow Brick Road, the Ruby Slippers. Star Wars is another of the quintessential myths of America. Other than the Wizard of Oz and perhaps Batman, it has the most characters and paraphernalia that are known to the average person on the street. I have theorized that Star Wars may potentially have a stronger reach in the West than the East, but who knows if the story
But speaking of Batman, a part of me thinks comic book superheroes might be the bread and butter of American mythology--many have theorized it's already the case. Superman and batman have the most mythic elements besides themselves to be part of the public consciousness. Villains, kryptonite, the bat-signal, etc. I think other characters that would appear, in order of likeliness, would be Spider-Man, Wonder Woman, The Hulk and Wolverine. (The last in particular around the Canadian regions) After that, I think we may see characters that fill niches, but may not be the same one. For instance a stretchy guy, a fire guy, that sort if thing. The may have continental popularity, but it wouldn't surprise me to see characters catch on in certain regions more than others. I can't help but think Superman in particular would be a symbol of the very American states.
What are other characters and heroes that would filter through the centuries? I mean, just think about how we have so many stories simply in a 100 years. Do we expect it all to last? Indiana Jones, I think could exist. Perhaps Buffy the Vampire Slayer. Even if the character has not become a major media franchise, she's probably the most well known of monster vanquishers. Perhaps something akin to James Bond, but filtered through a very American lens. (Absorbed into Jason Bourne? Jack Bauer?) In mind, the most enduring would be slasher monsters like Freddy Kruger, Jason Voorhes, the Alien, the Predator. Basically because they feel like such natural fits to previous folk stories. I've noticed the monsters of 80's horror movies seem to slaughter lustful teenagers or greedy corporations. Like morality plays on the seven deadly sins or something.
What's truly the rub with mythology, things don't stay exactly the same for hundreds of years. Would you believe Robin Hood, Maid Marian and Friar Tuck were their own separate legends, before being pooled together in one? So I've tried to be absolutely vague, and I suppose later I could come up with a more streamlined vision. But this has been what's been going in my head.