Tower 105 to Centex, Track 1

Amtrak's Texas Eagle uses the former SP station in San Antonio (so it can connect with the Sunset Limited). With Union Pacific's acquisition of the M-K-T as well as the MoPac, it has chosen to operate the former M-K-T and former MoPac lines between San Antonio and Centex, just north of San Marcos, as paired track. Track 1 (the former MoPac, ex-International Great Northern) heads north-northeast from Tower 105 (MP 260.4), across the Sunset Route from the Union Stock Yards, on a 20 mph Yard Limits track, past Apache Junction (MP 259.9), a flat crossing with the former San Antonio and Aransas Pass line, SP until 1996, which has a connector in the east quadrant. This connector from the Sunset Route to the former MP is west of the former SP station, connecting at Tower 112. This means that a Texas Eagle heading for Track 1 must either head southward out of the station, taking the connector northwest from Tower 112 to Apache Junction, or run in reverse to Tower 105, taking the connector in the southeast quadrant by the stockyard and then pulling forward across the flat crossing at Tower 105.

From Apache Junction, Track 1 heads north, past the MoPac San Antonio Yard, and the erstwhile MP San Antonio station (MP 259.1), where the Yard Limits end in favor of single-track, CTC, and the speed limit rises to 45 mph, and turns north-northeast past Adams (MP 254.0), northeast past the 7,559 ft. siding at North Loop (MP 252.1-250.6), within which is extra track at Towne Spur (MP 251.8), Green Light Spur (MP 250.0), Longhorn (MP 249.9, where the Longhorn Industrial Lead heads southeast, and Wetmore (MP 247.7), where the speed limit is 60 mph, turning east-northeast past a detector at MP 245.0, where the speed limit is 70-60, and the 8,428 ft. siding at Bracken (MP 241.1-239.3), and northeast to South Schertz (MP 237.8), where there is a crossover to North Schertz on Track 2, Ogden (MP 236.7), and Craig Junction (MP 235.9), where a connector trails in from Ogden Junction on Track 2.

The countryside north of San Antonio is lush farmland, since it is (just) east of the 100th meridian that represents the general boundary between the arid land to the west and the lusher land to the east. Also along the railroad between San Antonio and San Marcos are a number of rock quarries providing the kind of rock used in railroad construction and maintenance, as well as road building.

There is a 7,978 ft. west side siding at Corbyn (MP 235.0-233.4), where the speed limit is 60 mph, a dirt road grade crossing and a grade crossing within the siding, two bridges over roads, a sand facility on the east side, a grade crossing at the sand facility, sidings on the east side, a sand facility spur curves away to Track 2, a grade crossing, a closed dirt road grade crossing, the Western Railroad heads east at Dittlinger (MP 231.1), where the speed limit is 60-50, and the line turns east past two grade crossings, a road bridge overhead, two grade crossings, Brauntex (MP 230.8) and McCoy Lumber (MP 229.5), both places with additional tracks, to Landas Park (MP 227.8), where the speed limit is 30 mph for the flat crossing with Track 2 at New Braunfels (MP 227.7), where the line heads southeast past  a grade crossing just north of the flat crossing, four grade crossings in town, and a detector at MP 227.3.

The line turns turns north-northeast past two more grade crossings in town, a bridge over a street, a grade crossing, a bridge over a river, a plant on the west side, a grade crossing, Intermediate Signals at MP 225.6, a bridge over a road, a highway bridge overhead, two grade crossings, Coleman (MP 223.9), where the speed limit rises to 70-60, and a grade crossing, and northeast, just southeast of Track 2, past the 9,900 ft. east side siding at Goodwin (MP 223.1-220.9), a grade crossing, and Conrads (MP 220.7), where there is a crossover with Track 2.

At Jude (MP 219.0), there is a grade crossing and another crossover with Track 2, followed by a grade crossing, Hunter, a bridge over Track 2, which then curves and comes alongside to the east, a grade crossing, Intermediate Signals at MP 214.8, a grade crossing, and UP Junction (MP 212.0), where there is a track that connects back from Track 2 and a connector with Track 2 that trains headed for the former MKT line must take), additional track at H.E.B. (MP 211.6), a grade crossing, a road bridge overhead, a grade crossings, two bridges over streams, a grade crossing, and the platforms and shelters on the east side at San Marcos (MP 209.8 on Track 2), three grade crossings (the third is Glen Parkway), a bridge over a river, a grade crossing with a divided highway, and a grade crossing, before the final connector from Track 2 trails in from the south-southwest (i.e. the east side of the line) at the 8,249 ft. east side siding at Centex (MP 208.3, where the speed limit is 30 mph, past a grade crossing and a grade crossing at Pat Road, to MP 206.7, where it is 55-50), as the line heads north-northeast.

Approaching San Marcos, up on the hill to the west is San Marcos State University, its new high rises overshadowing the original two-story brick buildings where LBJ went to college and performed chores for the college president in return for lodging and board.