What concerns me more than the technical details is the dating.
The 49th parallel border was established in 1818, and even his 1500's date is well within the "historical" time frame.
If the Indians, of any tribe, were doing something this big, it would have been known to the Red and White men of the area.
Someone, somewhere, would have written about it.
He gives no historic account as to it's creation.
Not by either Red or White history.
As much as I like a good story, I have to come down on the side of "seeing what I want to see" this time.