This is a strange bit of disputed archaeology. Check it out over the web and Wikipedia does have a good description:
The Los Lunas Decalogue Stone is a large boulder on the side of Hidden Mountain, near Los Lunas, New Mexico, about 35 miles south of Albuquerque, that bears a very regular inscription carved into a flat panel. The stone is also known as the Los Lunas Mystery Stone or Commandment Rock. The inscription is interpreted to be an abridged version of the Decalogue or Ten Commandments in a form of Paleo-Hebrew. A letter group resembling the tetragrammaton YHWH, or “Yahweh,” makes four appearances. The stone is controversial in that some claim the inscription is Pre-Columbian, and therefore proof of early Semitic contact with the Americas.
The first recorded mention of the stone is in 1933, when professor Frank Hibben, an archaeologist from the University of New Mexico, saw it.