Thousands of stone tools crafted at least 10,000 years ago have been unearthed during a standard archaeological survey to clear the way for construction near a mall in US.
"We were pretty amazed," said archaeologist Robert Kopperl, who led the field investigation.
"This is the oldest archaeological site in the Puget Sound lowland with stone tools," he said.
The crews unearthed more than 4,000 stone flakes, scrapers, awls and spear points crafted at least 10,000 years ago by some of the region's earliest inhabitants, 'The Seattle Times' reported.
The discovery is yielding new insights into the period when the last ice age was drawing to a close and prehistoric bison and mammoths still roamed what is now Western Washington.
The site on the shores of Bear Creek, a tributary to the Sammamish River, appears to have been occupied by small groups of people who were making and repairing stone tools, said Kopperl, of SWCA Environmental Consultants.
Chemical analysis of one of the tools showed traces of the food they were eating, including bison, deer, bear, sheep and salmon.
The site near Redmond Town Center mall in Redmond, Washington was initially surveyed in 2009, in a project to restore salmon habitat in Bear Creek, which had been confined to a rock-lined channel decades before.
The first discoveries were an unremarkable assortment of artifacts near the surface, Kopperl said.
However, when the crews dug deeper, they found a foot-thick layer of peat.
Radiocarbon analysis showed that the peat, the remains of an ancient bog, was at least 10,000 years old.
"We knew right away that it was a pretty significant find," said Washington State Historic Preservation Officer Allyson Brooks.
