> you'd have to be a linguist to describe even one distinctly Oregonian accent, let alone dozens.

You could definitely describe two or three, but you picked a new, far flung, low-population state as an example. Britain has 14x the population of Oregon. If Oregon had two accents, you might expect Britain to have 28.

Going to older eastern parts of the country, you can usually tell where people are from within probably 100 miles. You can tell Chicago from Milwaukee from Detroit from Pittsburgh from Boston. You can tell Northwest Arkansas accents from Western Arkansas accents. You can hear a parent's Texas in the accent of somebody you grew up with in Kansas. You can even tell south Jersey accents from Baltimoreans if you ask them both to say the word "Orioles." Literally impossible for a Baltimorean to say. Orirols? Orals?

California has hella accents too.