Hi Tessa,
Thanks for sharing your photos and nice that you got to see such a large earthworm. 

As you may know, most earthworms encountered in Oregon are introduced species in the family Lumbricidae. Our large, native earthworm species are in the family Megascolecidae and they are seen less often. The largest documented native species is the Oregon giant earthworm, Driloleirus macelfreshi, but there are a number of other native Megascolecid worm species in the area too.
 
I am pretty sure that the large worm you found is one from the family Megascolecidae. A distinguishing feature is that Megascolecid worms have the reproductive band called the clitellum starting closer to the head end (usually around body segment 13), while non-native Lumbricid worms always have the clitellum starting posterior to body segment 18.

I'd guess that since the impressive worm you found is smaller than the size reported for the Oregon giant earthworm and you found it in the Coast Range, rather than in the flat part of the Willamette Valley, it is probably a different native earthworm. It would require an earthworm specialist to dissect the worm to determine the genus and species with certainty though.

Hope that helps!
Enjoy!