this guy is a great writer on the desert pre-history, and this is a great overview of the state of the
art.
interesting that the seed gatherers out-competed the hunters, and in-filled the great "starving lands" of the upper southwest.
this ties in wonderfully with the RMF story of the trappers, A collection of scoundrels" i believe it was...
there it is
http://books.google.com/books/about/A_majority_of_scoundrels.html?id=pOeRAAAAIAAJ
this is actually worth finding a hard copy. The maps (in back cover envelope) show how the area was grouped and settled by the river basins, and makes the scale of the travels even more amazing.