I'm not real knowledgeable on the low land Indians. If I recall the Coahiltans were coastal into Mexico? Anything is possible though and over the thousands of years they probably all followed the Rio Grande and had been everywhere. I do believe the pre-Aztec were New Mexicans at one time. They followed the Sun south to find out where it went every fall, and ended up down there..
Down past Judge Roy Beans place Dad went with some buddies to go jug fishing on the Rio G. He found a cave there up a bluff that had several stone metate's and a Sabre Tooth in it, with marked up wall. That was back in the 50's and such just wasn't as big a deal, so he left it there and was gonna go back later; never did.
Might have been Coah's.
The stone I posted was found in the Caballos foothills out in the open and was probably displaced. It is fairly soft thus I don't know if it would have survived the elements for more that a couple hundred years, but it's sure possible.... thanks for the reply.
G7