No one on this message board can give you a definitive answer whether an Amtrak employee will accept an expired passport. Amtrak policies require you to produce an ID on request to an Amtrak employee on board the train. It is not specifically required to board the train in the first place. However, there are several things to know:
1. Not all conductors make this request. IME you have a better than average chance of NOT being asked, but this is no guarantee. Other than
the conductor who lifts your ticket, it is extremely rare to be asked for an ID on board. If you are traveling from Georgia to Oregon, however, you
will be on at least three different trains, so that does increase your chances of being asked.
2. Amtrak's website lists
acceptable forms of ID. Please note that a photo ID is NOT specifically required, however the website does not
really list examples of acceptable non-photo ID's. And in any case, if you use a non-photo ID, you need to have TWO pieces of ID, one
of which is issued by a government entity.
3. If you use an expired passport, there is a pretty good chance that the Amtrak employee will not notice the expiration date, unless the photo is
obviously (i.e. 20 or 30 years) out of date.
4. As the previous poster said, expired passports do have some legal standing as acceptable ID forms, but an on-board Amtrak employee may
not be aware of this. In any case, Amtrak's website says to be valid, an ID has to be "current and in-force."
So I would GUESS you would be fine. But as this board is not specifically associated with Amtrak, we can offer no guarantees.