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The most likely scenario here, is that Travis was sold a map, not stone, and he found a number of clues that convinced him it was a true waybill. One of the people he met around the mountains had to be the author. After following the map and finding many of the symbols and markers right where the map showed them, and yet no treasure.
His supposed area of search was away from the area he actually searched, as he still felt something might be there. He came to realize that a book and some dramatic forms of the map's were his path to some measure of wealth. They would finance his real area of interest. He never found a buyer or completed his book before his death. It was his wife who finally found a "sucker".
Just one man's theory.
Good luck,
Joe Ribaudo.