Not covered by a USRail pass, but if you ever get the chance, take a day-trip on the Cumbres & Toltec narrow-gauge railroad: [link] . I had a wonderful time with them.
I've also heard good recommendations for the Durango & Silverton railroad, but I haven't been on that one myself (yet): [link]
And someday I want to take the Rocky Mountaineer: [link]
I was just talking about the Rocky Mountaineer with my dad. I do want to slip in an Acela ride this trip, I think, but I mostly want to cover a lot area so I don't know that I'll have much room for other non-Pass trains. Intriguing idea, though!
I do expect to get out near you, JenP! I want to kind of circumnavigate the available railway system as best I can. It's 10 segments in 30 days which has a lot of possibilities as, for example, the Zephyr from Calif to Chicago is one segment (which is how I originally planned to start this trip when it was entirely theoretical because I had never taken the Zephyr, but now I have so maybe I will head in a different direction first. SO MANY OPTIONS