This line, as the Santa Fe Northwestern Railroad, branched from the AT&SF mainline at Bernalillo, NM, and ran to San Ysidro where it split into two branches.
The first branch was constructed to harvest the large Ponderosa Pine trees, and was run by the New Mexico, Lumber and Timber Company; portions of the old grade are the base for State Road #485 which turns into Forest Road #376, providing vehicle access into that portion of the Santa Fe National Forest. Two tunnels above Gilman, NM (once the sawmill and camp) are excellent examples of the engineering necessary to construct rail into this rugged region. Some remnants of the grade are sporadically noted from some of the forest access roads in the canyons.
The other branch, known as the Santa Fe, San Juan and Northern Railroad, went northwest from San Ysidro and terminated a few miles north of the (now abandoned) settlement of La Ventana and served some coal mines until their closure in the Great Depression. It had been planned to run this branch through Cuba, NM and on to Farmington, NM but was never constructed.
An excellent history of these lines along with a hand-drawn map can be found at the link below.
Thanks to Dr. James H. Olsen, Jr., PE for contributing information about this route.