Well, then I'm confused.
You started off saying that it makes sense for these people to say that the government of Idaho upholds American values more than the government of Oregon, because values' 'Americanness' isn't determined by the majority, but rather by appeal to ancestry and tradition.
But apparently the Chinook (or, if you wish, the Paiute), who I would say have superior claim on that front, don't get to wield the mystical power of American Values because they were never numerous, nor influential.
But surely the population of Idaho and eastern Oregon is also not particularly numerous, nor influential.
And the population of Western Oregon also, surely, has some claim to be a "significant fraction of the population", "disproportionately descended from ancestors who have been American for many generations", so surely that means their values are more American values than ones which fail one or more of these criteria?
So I guess I just don't know what gives these people of Eastern Oregon more of a claim to determine whether Idaho or Oregon is 'more aligned' with American Values. Is it because their ancestors have been Americans since the early days of the old West, and they embody the pioneer spirit of the Oregon Territory? So their values are more American.
But it's maybe worth noting that in 1844, while Frederick Douglass was first publishing his slave story, Oregon passed a law that made it illegal for him, or any other freed slave, to set foot in the state. It remained part of the state's constitution through its admission to the US, and long after the 14th amendment made it unconstitutional.
In 1926, thirty years after Frederick Douglass died, a ballot measure to repeal it was finally passed. But 32% of voters voted against it.
Maybe if white supremacy is 'surely' no longer an American value, we shouldn't be looking to the traditional values of Oregonians as a guiding light. They have a bit of a history of being slow to catch on to changes in what are 'surely' American values.