I don't know about Shortstack, but, yeah, that idea is active in my noggin - and yours too, it seems. The Michigan copper mystery is very, very interesting, and if you consider the difficulty in logistics getting there from the Mediterranean, plus the Mexican Phoenician discoveries - and that Arizona cave anomaly too - well ... hello! Getting into the Southwest is almost a no-brainer.
The usual route conjectured into the Southwest was via the mouth of the Rio Grande. The river was navigatable in that age, and could have been followed to today's Organ and Caballo ranges (hmmm) - and to the Rio Puerco too, for that matter. The means of travel are apparent, but the big question is whether they were merely exploring or had maps to specific destinations.
I've been meaning to bring this up for awhile, but i've always wondered if they ever used the Rio Grande to transport their goodies to the Gulf of Mexico. I know mr Don Jose has mentioned that the goods were transported to a small bay just south of the Texas border for shipment, and I have read about that elsewhere. The river, like mr Springfield mentioned, was navigatable in those days. Curious what you guys and gals think about that possibility. Plenty of places to hide the stash along the way if need be.....maybe some left behind along the way?....hmmmm.