In 2007, a Snohomish County developer discovered thousands of artifcats that archaeologists place at up to 9,000 years old. For some reason the story is just breaking now. Here's coverage in the Everett Herald and from KING 5 News. The location isn't being reported, to deter members of the public from picking up souvenirs.
When people think Pacific Northwest, Washington, Puget Sound, or Seattle history, they often go back as far as 1774, 1792, 1805, 1841, 1848, or 1851. This discovery is a reminder that there were people here before the settlers, and that we really should begin thinking of our local history as beginning sometime around 7000 BC.