Evidence from the Cooper's Ferry archaeological site in western Idaho shows that people lived in the Columbia River Basin around 16,000 years ago. That's well before a corridor between ice sheets opened up, clearing an inland route south from the Bering land bridge. That suggests that people migrated south along the Pacific coast. Stone tools from the site suggest a possible connection between these first Americans and Northeast Asian hunter-gathers from the same period.
Route closed due to ice
A piece of charcoal unearthed in the lowest layer of sediment that contains artifacts is between 15,945 and 15,335 years old, according to radiocarbon dating. More charcoal, from the remains of an ancient hearth pit, dated to between 14,075 and 15,195 years old. A few other pieces of bone and charcoal returned radiocarbon dates in the 14,000- to 15,500-year-old range. In higher, more recent layers, archaeologists found bone and charcoal as recent as 8,000 years old, with a range of dates in between.
This makes clear that people had been using the Cooper's Ferry site for a very long time, but it's hard to say whether they stuck around or just kept coming back. "Because we did not excavate the entire site, it is difficult to know if people occupied the site continuously starting at 16,000 years ago," Oregon State University archaeologist Loren Davis told Ars. "I expect that this site was used on a seasonal basis, perhaps as a base camp for hunting, gathering, and fishing activities."