It was a Carter Family adaptation from the 30's; check the Carter Family sources threads for more information. My brief notes, gleaned from Charles Wolfe and the sources thread (info from Q?) say:

Sara [Carter] thought they learned it off a Victrola record. Cowboy Jack Laws B24: was first published in the 1928 Songs of the Open Range. It was recorded three times in 1929 first by Marc Williams for Brunswick. The earliest recording was Jack Mathis for Columbia. The song actually is a rewrite of "Your Mother Prays for You Jack" by F.M. Eliot in 1893. [Note the difference in title from what Q gave above, though my notes may be wrong.]

Having no access to the original sheet music, collection or recordings mentioned, I can't guess to what extent the Carters modified the song, but their version (possibly including the tune) is still copyrighted, and the collected versions I've heard (all post-30's) stem from the Carters--caveat singor.