@Mor - Not to take away from Oregon's decision to name the beaver as their state animal, but I think the beaver is one of their more unique animals, just because it is so endangered.
They also have things like black bears and longhorn sheep, which might have been contenders.
But, the beavers do stand for hard work and industry as well as cooperation within a group. And the Oregon state motto is "she flies with her own wings" which I always took to mean that they manage to succeed and thrive with their own resources.
The beaver is a perfect symbol to match that kind of attitude.