If it is giant hogweed, the invasive plants people in the area usually appreciate it if you let them know.
On the other hand, poison hemlock looks pretty similar, and although it is a non-native weed, it isn't noxious enough that the county will send someone out to destroy it. In my experience it's a little more common than hogweed.
Well that may be it. There's a place up in Umpqua called Hemlock Lake. There's definitely a lot of hemlock out there too. But I wouldn't trust myself to differentiate, but can say that some of the really big plants looked exactly like the pictures you linked.
