Can someone to explain why Northwest states (I mean only Washington and Oregon) are fairly liberal? Huge majority of population is white and there is a little minorities. (quite much Asian though) So there is no "natural" reason for this blooming of liberalism.
Of course Democrats' support is concentrated Seattle's and Portland's metropolitan areas, but there is also pretty liberal areas in Washington rural coast region (some poor fishing villages, I assume) and in western Oregon. In Dave's election maps there are lot of red colour in these rural areas at least since 1960. (As your know there is no countylevel information before 1960 in Dave's pages)
The reasons for the liberalism in the Northwest are complicated, but one thing you mention interests me. As you say, the Northwest is very white, with few minorities. The same could be said of places like Minnesota, Wisconsin, and some of the liberal states of New England. Many Southern states, which are only 60-70% white are strongly Republican in spite of near total Democrat voting by the minority groups. Also, even California, which is very Democratic has a very large percentage of its white minority that are conservative Republicans. The obvious generalization is this - whites are more liberal when they are living in segregation, and much more conservative when living with other races.
That might hold true in some situations, but of course whites in NY are quite liberal, and whites in the lily-white states of ID, UT, WY, ND, etc. are quite conservative.
