As far as glaciation; I thought it was glacial movement along what is now the New river, in Va. blocking the river up causing spill over that moved the brookies to the southern part of their range. Hence the differnce in Southern Strain versus Northern Strain.
Now as to elevation not sure of the Smokies, but do know in my little areas of Va. that the were the primary "game" fish in the Shenandoah during the colonial period and up till the Shenandoah Valley became the Bread Basket of the nation in the late 1820ies-the Civil War when the yankees destroyed the area to starve out the southern states. On the east slope (in the little area I used to familiar with) they made it down to the Junction of the Rappahannock and Rapidan Rivers.
Natural barriers are mainly circumvented during high water events. This is one of the biggest threats to brookies now in the SNP. Changing the course of the streams to prevent flooding, deforestation at low elevation, and huge silt loads at low to mid elevation from logging, and devlopement cut the brookies off from migrating into new or previously inhabited streams. It also seals off populations and causes bottlenecking of the gene pool.
There was a huge article on this subject in a rescent fly fishing mag. Glad to see someone interested in this subject. Out west where the Army has moved me they are refered to as Colorado bluegill. I guess the name is justified though, their population here is astranomical and they are an invasive speacies that out competes the native cutties.
Have a Good 'Urn,