CA will honor Oregon registration. I've actually been checked quite a few times, mostly places where you pay a fee like the CA state run places, been checked in the national forests a few times as well. Sounds like a fun place, I might have to take a trip up there sometime.

 

We used to ride in the Hope Valley area and a couple years ago a wannabe (volunteer) ranger threatened to write us up and sent us back to camp with a warning because we were fron Nevada and did not have out of state california green stickers. Since than, I found out these can be purchaced in most of the bike shops in the reno area. Might check w/local shops in Oregon.