Yes, Least Weasels, If you look them up they are supposedly not in WA but many years ago I caught some. It really has to be somewhat of a fluke to catch one because they are tiny. Practically impossible for them to set a trap off but I had them really weak 1 1/2s back 45 years ago.
They are completely brown even on the belly and have a stub tail. Length is 4 or 5 inches. Body is about the size of your thumb in girth.