The idea that Frontierland only ever included the old west has been false from the very beginning.
In the "Disneyland" TV show Episode 1 from 1954 prior to the park opening, Walt Disney described the different lands and what they were going to represent. Nowhere in the description of Frontierland did it state that it was only the western states. Walt stated that the land is the "Inspirational America of the past century, the treasure of our native folklore. The songs, tales and legends of the big men who built the land." Behind Walt was a map of the United States, with a bunch of classic traditional American characters (real and fictional) from said era scattered across the map. Not just the west. They then tie this directly into a promotion for the upcoming Davy Crockett film which is set in Tennessee.
On opening day at Disneyland, Frontierland encompassed deep south states, not just western ones. Davy Crockett being a famous Tennessean. Mike Fink ran boat transportation between Ohio and Mississippi. Mark Twain was born in Missouri, and that's also the state that Tom Sawyer lives in. The Mississippi River is also the border connecting directly to several other deep south states. Country Bear Jamboree is also Tennessee.
The ONLY awkward element about Splash's placement in Frontierland is Pecos Bills. That could and should have been addressed, though also not as big of a deal as people make it out to be (and certainly not remotely as big of a problem as Tiana's placement/setting). Otherwise, the attraction was a very good fit for the land.
I was referring specifically to that posters suggestion that WDW's Frontierland was based around "The Four Corners", which is the region where Arizona, Utah, Colorado and New Mexico all meet. Splash Mountain was very certainly not themed to any of those.
However, it should be noted that Disneyland's Frontierland and WDW's are
not designed and themed the same way - Frontierland as a concept is not automatically exclusionary to tales of the South or even the East, but
WDW's Frontierland was constructed very carefully to chart a Western progression with its structures and landmarks.
It is true that the buildings and attractions on the The Rivers of America waterfront were designed from opening day to reflect the geographical thrust of the nation - Liberty Square mostly represented the original Colonies along the East Coast, with Frontierland representing the Western states, both divided by "The Little Mississippi" waterway. Starting in the Northeast corner and working your way down and around, The Haunted Mansion represented Upstate New York, The Nantucket Harbor House (Now Columbia) is obvious, The Hall of Presidents Philadelphia, Liberty Tree Tavern Williamsburg, then starting to move westward with The Diamond Horseshoe representing St. Louis, the "Gateway to the West".
Notably, Liberty Square was elevated a good bit above River Level, so that as you stood in the Square proper the view of the Riverboat was almost completely concealed by the high grade and the Riverboat Station building - it was known the Riverboat was most appropriately seen in Frontierland, despite the operational necessity that it pass Liberty Square. That's why the Landing was placed
in LS, to keep the vista open to see it once you've entered Frontierland. That's a strong bit of intentional staging that doesn't get much mention, done in support of the desired geographical journey for the guests.
From there you crossed from East over The Little Mississippi to West into Frontierland, with all the opening day placemaking and architecture becoming decidedly and exclusively Western. The Frontierland entrance stockade, the Frontierland Shootin' Arcade, and Frontier Mercantile all set the early tones for Western expansion, where buildings were starting to be built from both logs
and stone, suggesting both the resources as settlers traveled west, but also suggesting growing and intentional permanence. Continuing west the buildings start to become more expansive and elaborate in their design, their architecture and materials both further affirming the settling of the Western territories.
The Country Bear Jamboree has always been described to me as representing the great cabins of the Colorado Rockies, so I'm not totally sure where the idea of it representing Tennessee comes from (There
is Tennessee Bear in the show, of course, and the
new show has been described as recalling Nashville's Grand Ole Opry, but that's the new show, not the original - and not the architecture). The General Store and Prairie Outpost are fully Western constructions down to the wooden Native American out front.
The Mile Long Bar literally said Saloon above it; Hard to get more explicity Western than that. Next down the line, similary, is Pecos Bills Cafe (Mile Long Bar was absorbed as part of the Pecos Bill expansion in the 90's), which is similarly self explanitory. Both the inside and outsides of all the buildings on this strip supported distinct and committed Western stylings. At one end of the building is the Town Hall facade, the other end is constructed from Adobe Brick. The interior was and is full of different shades of Western, but they are all Western.
I've heard of the original Frontierland Train Station being designed to look "Californian", but admittedly the building was so relatively simple it's hard to see any real sign of that influence, so I don't particularly assert that. I'd describe it as less explicitly styled than anything else in the land, though not incongruous with the Western town they built.
From there the stage was set for expansion further north - The original plans for Frontierland accounted for Western River Expedition and Thunder Mesa, which of course never came to pass. The space went to Big Thunder, but that does still fulfill the intended idea of representing Monument Valley, bordering Utah and Arizona.
Tom Sawyer Island was itself
not an opening day attraction, opening instead in 1973, but because of its existence at Disneyland I'd imagine it was given consideration from the outset. Tom Sawyer takes place in Missouri, slightly West of St. Louis, so given the Island's placement encircled by the Riverfront sections of Frontierland and Liberty Square it makes decent sense. I'll give you that the Dock is not perfectly placed where it is over by Big Thunder, though the building is hardly more than a humble shack.
I'll also give you that the Attraction interiors do, of course, stretch at times beyond the unity of their exteriors. It
is the Magic Kingdom after all. Hence the Talking Bears, Ghosts, and perhaps most ghastly, contemporary Presidents who make appearances within. But the Architectural continuum of the facades from Liberty Square through Frontierland was perhaps the most intricate piece of early Walt Disney World placemaking, creating a conscious and overarching thematic passage that sustained integrity across the two lands adjoined around the Rivers of America. Eastern properties east of the Mississipi, Western west of it, and they really didn't quiver on the matter.
I don't buy the idea that Splash's placement is "not remotely as big of a problem as Tiana's placement/setting". I'd say that they are pretty equally inappropriate, given the effort that went into developing the thematic landscape of WDW's Frontierland and how conflicting both are with that. But I would also say the damage was most certainly done by Splash 32 years ago, not by Tiana's today. At this point the seal has already been thoroughly broken. Which doesn't mean it wouldn't be ideal for them to repair that, just that it doesn't make sense to blame the successor to what broke it instead of what actually broke it.
