Hey, Joe, I posted another long screed on "Away Rio!" a few minutes ago and it vanished!

What I can remember:

An 1868 shanty article says that "Rio Grande" "is perhaps the greatest favorite" of them all. The article quotes one stanza, proving that it's this song.

That's the earliest reference to the song know to exist.

No one explicitly mentions hearing the song before that date and Alden, writing in 1882 about shantying in the '50s, doesn't mention it.

A great song like this must have traveled fast - another reason to consider that it may have originated in the '60s.

The evidence either way is so scanty as to be inconclusive.

Right now, though, 1868 is the year to beat.

PS: "The Song of the Memphis Volunteers," a minstrel song anout the Mexican War in "National Songs, Ballads, and Other Patriotic Poetry" (1846), ends (almost) with the lines "We are bound for de Rio Grande. We are bound for de Rio Grande." But the tune is given as "Lucy Neal," which as far as I can tell bears no resemblance to the tune of the shanty.