This pupa was found under a rock in the stream (Wilkeson Creek). I had to disturb the tiny bits of gravel that were adhered to the rock surface. This was inside that little gravel "cairn". My second photo shows the pupa next to what's left of its gravel cairn.
I'm pretty sure this is a caddisfly pupa. See http://www.flyfishontario.ca/ontario-fly-hatches/hatches-of-ontario/caddis-flies.html and http://www.troutnut.com/specimen/560/. Which caddisfly I do not know, although Limnephilidae seem to be common Washington.