While I'm not sure how they would route you, it is my understanding that any valid Amtrak trip is bookable via AGR. The key is that you can't book trips that lead to stopovers when other alternatives are available. If there is no other alternative, then the trip is bookable via AGR even if it requires an overnight stay. So for example, NYP to HOU would require an overnight in New Orleans and that is a valid trip for AGR.
What you can't do is to say you want CHI to PDX, via Seattle since there is a valid alternative, namely taking the EB directly to PDX.
In your case Yarrow, it sounds like you can do it on a one zone award, but you will end up on a San Jaoguin and a bus.