Andrew
I think you are getting a lot of good advice but if you are looking for a local hardwood we don't have that many choices in the Puget Sound basin.
According to the Forest Service (whose focus is commercially valuable timber) the choices are;
Red Alder
Oregon Ash
Western paper birch
Black cottonwood
Pacific Madrone
Bigleaf maple
Willow
Alder would be my last choice as a building material; it is soft (for a "hardwood") brittle and anything but straight grained. And if used outside it can be called by another common name…compost.
Of the list above my candidates would be Ash, Birch, Madrone (Arbutus for our Canadian buds) and Maple, probably in that order for strength and straight grain. The Ash, Birch and Maple are all species that you should be able to find in the Skagit valley as they are low elevation/river bottom trees.
The Madrone grows closer to salt water, the folk wisdom being that it must smell the salt.
Madrone would be my choice for appearance; it has a beautiful butterscotch color. You do want to work it green, once dry it is very hard.
There is a species of oak in the region, the Gary oak, but this is associated with the south sound prairie ecosystem and is very limited. And for that mater probably endangered in the area
You might also find Black locust which is a none native invasive species with excellent characteristics, one of which is someone will be happy to part with it.
Good luck
J.E.B.
