Lois, if you are planning on driving the N. Cascades highway anyway, the
best place (most reliable?) to see Three-toed Woodpeckers is along the
trails to Lake Ann or Rainy Lake at Rainy Pass in Skagit County. These
trails are very well marked and easily accessible (and usually crowded).
These birds are quiet, so you might have to wait awhile before seeing one.
But I'm 3-for-3 at this spot. Each time, it wasn't until one flew that I
finally saw it (and then, each time, it was high in a tree in a
difficult-to-view spot), so patience is probably necessary.

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Michael R. Smith
Univ. of Washington, Seattle
whimbrel at u.washington.edu
http://salmo.cqs.washington.edu/~wagap/mike/mike.html