Archaeologists have uncovered a stone tool at an ancient rock shelter in the high desert of eastern Oregon that could turn out to be older than any known site of human occupation in western North America.

The find was announced Thursday by the U.S. Bureau of Land Management.

University of Oregon archaeologist Patrick O'Grady, who supervises the dig, says the site outside Riley has not been fully excavated. But the tool, chipped from a piece of orange agate, was found below a layer of volcanic ash from an eruption of Mount St. Helens 15,800 years ago.

Bureau of Land Management archaeologist Scott Thomas says that if the date proves out, it would be another predating the so-called Clovis culture, once generally believed to be the first people to migrate from Asia into North America.

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