The original poem, "A Border Affair",was written by Charles Badger, at about the turn of the last century (no, the last last century). It had some politically incorrect content: "..She wes Mex and I was white, Like as not it's better so..), and was cleaned up in the 1940's for refined political sensibilities. Richard Dyer-Bennett, I believe, was responsible for both the song's resurgence and som of the modifications. I have no idea where the tune came from.