Waldo to Rosario
This abandoned line used to be the actual mainline of the Atchison, Topeka and Santa Fe through New Mexico, laid in the 1880s. In 1970, the Army Corps of Engineers decided to construct the Galisteo Dam directly across the right-of-way at a point southeast of Rosario, NM, for the purposes of flood control. The AT&SF line was consequently relocated to the north, starting at Waldo, NM, and rejoining the former mainline to the west at a point northwest of Rosario. The former mainline between this junction and Rosario is still in use today and serves gypsum mines at Rosario.
Thanks to Dr. James H. Olsen, Jr., PE for contributing information.
I found an even older mainline alignment that departs Rosario heading northwest, clocked just slightly more towards the west than the current Rosario spur. There's a bridge abutment and a pier where it crosses the Galisteo on the east side of I-25. Then it crosses the highway and there's more piers where it crosses back over the Galisteo and reconnects with the current mainline a ways down further. The newer way cuts through a hill to avoid the two extra river crossings.