Geological WI: Fewer and less passable Appalachian gaps

A song on the radio about Daniel Boone's Wilderness Road got me to wondering about this. The closest I could find here was this. However, that's a rather different scenario, and the discussion is about the

What if there were significantly fewer gaps or passes across the Appalachians? Let's say the Hudson River and Mohawk valleys are as per OTL. The other water gaps are still there, minimizing the ecological effects, but more difficult to pass through (say, due to rapids or other obsticals like the Great Red River Raft). And the wind gaps, like Cumberland Gap, Buford's Gap, Culver Gap, Big Gap, Thornton Gap, Swift Run Gap, Manassas Gap, and Rockfish Gap either don't exist or are equally more difficult to pass.

I'm assuming this will slow down the British/American expansion westward. Maybe even enought to butterfly away or delay the 7 Years War? Also, it might allow the natives time to consolidate.

What effects am I missing?
 
Looking from a preColumbian POV. It's possible that there would be less contact and trade between the Mississippi civilization and the coastal cultures, so concievably they may be less advanced. The spread of maize slowed in some regions?
 
I do love these Geological PODs. While granted everything would be completely changed so possibly no British or French as we know them but anyway. I think this forces contact into a few small areas therefore it would be manageable for any colonial overlord. secondly, the people on the coastal side would be mostly isolated from the plains and thus would probably develop a more independent culture.
 
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