Actually, there's two trains which both start at Alamosa. The San Luis Express, which is the train you're thinking of (and is the one that the 1744 is scheduled to pull), runs from Alamosa to the town of La Veta and back. The Toltec Gorge Limited runs on weekends south to Antonito, where passengers can connect (in theory, at least) with C&TS trains making the round trip to Osier and back. However, there isn't a joint ticketing arrangement in place which guarantees that one will actually be able to transfer between the two trains all of the time, even though you can (supposedly) buy tickets for both trains online through the official website for the SLRG passenger trains (despite what the site claims, you actually can't buy tickets for both online - just for the SLRG train - and although it says you can make the transfer, the Cumbres & Toltec website makes no mention of this or even the SLRG passenger trains, for that matter). What I've heard about the 1744 running to Antonito is mostly rumour at this point; I doubt it will actually make any scheduled runs to Antonito this year (except perhaps for one or two special trips), but charter runs are certainly possible.