The glacial till in Western Washington almost everywhere does contain microscopic gold. It is difficult to recover. Gold is where you find it, and you may find a paystreak in any of the local rivers, or in black sand areas along the beaches. Gold was once mined at Crystal Mountain. Placers have been worked on the American River, and the Raging River near the I-90 bridge at Preston. Some nuggets have been found in the Beckler River near Skykomish.
I would recommend joining a club if you are interested in gold panning. Here is a group that have some claims: http://www.washingtonprospectors.org/
