The Santa Fe Southern is the former ATSF Santa Fe Branch, operated as a short line and tourist railroad, and soon (2006) to be used, in large part, for the entry of New Mexico's "RailRunner" commuter trains into Santa Fe.
The line starts out from the former ATSF depot (facing the old D&RGW "Chili Line" depot, now a restaurant, across the parking lot to the east), on the southeast side of the line near MP 18 (the end of the line is at MP 18.1), where there are four parallel stub-end tracks, with a dock on the east side of the third track from the east, heading southwest and descending steadily, with a 5 mph speed limit, through Santa Fe, with the four tracks reducing to two (with the two westernmost stub-end tracks only having access to the western track). There is a short spur on the west side, and an extra track starts from a stub end on the east side, at a location known as Wholesale, with these three tracks crossing Paseo de Peralta at grade. The two through tracks reduce to one and the speed limit rises to 10 mph, with the eastern track trailing into the western track, and then the east-side spur trails into the remaining track, before the latter crosses the intersection of Cerillos Road and Saint Francis Drive at grade near MP 17.4, after which the speed limit rises to 15 mph.
The single track crosses Cordova Road at grade, and throws off a facing spur on the west side near MP 17 that serves Copar (Big Chief). After crossing Alta Vista at grade (10 mph on the crossing), a short spur serving the highway department trails in on the west side, a siding serving general Pumice departs and then trails on on the east side, and a short spur heads away into the Santa Fe Southern Yard on the west side. The line then crosses San Mateo at grade, and turns south near MP 16, crossing Saint Michael's Drive at grade, bridging over an arroyo at MP 15.6, leveling out and crossing Siringo Road at grade, and then curving southeast and bridging across an arroyo at MP 15.0 (10 mph on the bridge), before turning south and crossing Zia Road (US 84) at grade.
South of that crossing, there is a facing spur on the east side serving C.R. Minerals on the east side of St. Francis Drive, a bridge over an arroyo at MP 14.5 as the line curves southwest again, a spur serving Premier ABC Supply (the line's major customer—an Anheuser-Busch bottling plant), also to the east of St. Francis Drive, trails in on the east side, there is a bridge over an arroyo at MP 14.0, the line turns south and crosses Rodeo Road at grade and then passes beneath the dual concrete bridges of I-25, all still in the urban area. The speed limit rises to 20 mph, and the line crosses Old Agua Fria at grade into an area of scrubby hills outside the city of Santa Fe, passes MP 13, turns east and descends to a curving bridge over an arroyo at MP 12.6 (10 mph on the bridge), after which it starts to climb west-southwestward to MP 12, turns southeast on the level past MP 11, where there is a large water tank to the west of the line, bridging over an arroyo at MP10.8, crossing Leaping Powder Road at grade, bridging over an arroyo at MP 10.4, where it starts to climb again, and another at MP 10.0, turning south, southeast past the end of Nine Mile Road and bridging across an arroyo at MP 9.4, and starting a descent that continues for the rest of the way to Lamy.
Past MP 9, the line turns southeast briefly, to a bridge over an arroyo at MP 8.1 and passing MP 8, before settling in for a curving run southward, bridging over arroyos at MP 7.4 and MP 7.1, passing MP 7, crossing Avenue Vista Grande at grade, passing through the sparsely scattered housing of El Dorado, bridging over an arroyo at MP 6.1 (10 mph on the bridge), passing MP 6, bridging over an arroyo at MP 5.7 and another at MP 5.2, passing MP 5, crossing Avenue El Dorado at grade, bridging over an arroyo at MP 4.8, passing MP 4, bridging over an arroyo at MP 3.9, crossing Spur Ranch Road at grade, bridging over an arroyo at MP 3.2, and passing MP 3.
The line turns briefly east, with the speed limit falling to 15 mph, and then southeast as it starts to descend much more steeply, through an area with cuttings and embankments, bridging over an arroyo at MP 2.2, passing MP 2, and then turning roughly east , across US 285 at grade, to MP 1, where the speed limit falls to 10 mph, and then southeast, as the grade slackens, bridging over an arroyo at MP 0.5, and turning east, across County Road 33, to Lamy (MP 0), where there is a wye, a short siding and spur on the northeast side of the wye, and a junction with the former ATSF passenger main from each end of the south leg of the wye..