A married man asks (Katie) to marry him and go "across the Blue Mountain to the Allegheny." Katie's mother tells her to let him stay with his own wife. Katie answers, "He's the man of my heart." (The confused ending may tell of her poverty or abandoment)
Abrahams and Foss note that the several versions of this song (they print four, all of which reportedly use the same tune) are from the same area -- central Virginia, on the eastern slope of the Blue Ridge. (The Alleghenies can indeed be seen from the crest of the Blue Ridge.)
Their four versions were all collected in 1962, from an interesting list of sources: Florence Shiflett of Wyatt's Mountain; David Morris, also of Wyatt's Mountain; Effie Morris, of Shiflett Hollow; and Marybird McAllister, of Brown's Cove.
The four versions fall into two types. The two from Wyatt's Cove end with a moralising conclusion (the girl ends up "lame" and perhaps abandoned, and regrets her ending). These stanzas have a slightly different feel from the rest of the song, and are much poorer poetry; one suspects a later addition.
On the other hand, the other two versions do not have a proper resolution; the girl simply wishes she could be with the fellow and "valleys" (envys?) the woman who will be with him.
Portions of the song seem older (e.g. all four versions have as their second verse the stanza "I'll buy you a horse, love, and a saddle to ride," which comes from "High Germany" or something similar). One suspects that a local Blue Ridge balladeer reshaped an older song to describe a now-forgotten local event.
At least, it's probably forgotten. There is a story in Walter R. Borneman's _1812: The War That Forged a Nation_, p. 15, about Harmon Blennerhasset (1765-1831). Born in Ireland, he eloped in 1796 with an 18-year-old girl. Meeting disapproval at home, he sold his estates, moved to the Americas, and after a brief residence in the east, crossed the Alleghenies with the girl. Reading the story, I was instantly and strongly remined of this song.
Of course, the details differ. One difference is substantial: The reason Blennerhasset was shunned was because the girl he eloped with was his niece. And he ended up returning home to England; he was caught up in Aaron Burr's Louisiana conspiracy. I don't really think Blennerhasset inspired this song, but it was interesting enough to form the basis for an idle footnote. - RBW