There is a legal way to do this:

New States may be admitted by the Congress into this Union; but no new State shall be formed or erected within the Jurisdiction of any other State; nor any State be formed by the Junction of two or more States, or Parts of States, without the Consent of the Legislatures of the States concerned as well as of the Congress

— Article IV, Section 3, Clause 1

Nebraska and South Dakota have a compact that’s been approved by Congress that has land swap between the states based on where the river is when particular assessments happen. So land leaving one state and going to another state isn’t unheard of. If you go look at NE and SD’s border in the southeast corner of SD, you’ll see the river and the border is pretty tight. Now compare that to states that have no such compact like Arkansas and Tennessee. River and the border are all kinds of messed up.

The thing is, both Idaho’s and Oregon’s State assembly will have to vote on it as you indicated. It’s not up to the citizens to dictate when a state’s border can be redrawn. Once Idaho and Oregon have a compact, they will need to send it to DC for Congress to vote on it. If it passes both the House and the Senate, the new compact can be enforced and the new borders drawn.

From what I’ve heard Oregon will not even begin to entertain this notion.

But yes, this is completely legal in the Constitution and we’ve done it before too. And we even have had the case where we took one state and split it into two happen before as well. Virginia and West Virginia. So we’ve used this part of the Constitution enough to know exactly how it needs to go down.

Is it going to go down? IDK. California said they were going to split up into 3, 4, 5 different States, not holding my breath on that one either. Would be pretty neat to redraw Idaho though. Never liked it’s weird long edge on the west side. Now it’ll look like someone giving the middle finger or something.