Wow! Someone just released a fan art map that shows exactly what I was talking about. The water level is a bit higher than I would have made it, but still very cool. Check it out...
I had forgotten about the rock salt description and the Zora stone monument. Your other points are great as well. I agree that the ridge could very well be the product of tectonic activity, but again the strange thing about that is that it cuts of the river at its mouth rather than its source...
I'd love to see a map with a raised water level based on elevation. It's not that much of a stretch if you consider the elevation of the Akkala Highlands, Death Mountain, and the Hebrin Mountains. Either way, that northeastern plateau is very strange.
I posted this as a comment on the Leviathon Bones thread, but thought i warranted it's own thread as a theory. I was just looking at the BotW map and thinking to myself that there is a TON of geological evidence that a great portion of the map was covered by water at some point. The most...