Flatonia is the location of a major intersection both on the former SP and today's UP, where a major freight flow turns away north at the single track flat crossing at MP 97.3, with single track connectors in the northwest and southeast quadrants. The line to the north is the former San Antonio and Aransas Pass line to Hearne and the Cotton Belt connection at Corsicana, whose importance can be judged from the fact that the Flatonia subdivision turns away from the Sunset Route to head northwards to Hearne on the northwest quadrant connector, while the Sunset Route continues east.
From Flatonia, the Flatonia sub. heads just east of due north, curving to the north, single track, CTC, with speed limit 70 mph at the junction, past a turn north-northeast, north, north-northeast, a detector at MP 91.9, where the speed limit is 50 mph, the 9,600 ft. siding at Muldoon (MP 89.0 - MP 88.1), where the speed limit is 60 mph and CTC gives way to Track Warrant Control, Automatic Block Signals, Marly, Lena where it turns north, a detector at MP 80.6, where the speed limit is 55 mph, the flat crossing with the UP (former M-K-T line from San Marcos to (originally) Houston at West Point (MP 77.0), where the speed limit is 45 mph, a turn to the north-northeast, a bridge over the Colorado River, the 8,602 ft. siding at Winchester (MP 73.5), where the speed limit is 55 mph, and a detector at MP 70.6, where the speed limit is 50 mph.
The line turns just west of due north, to Northrup, and then curvily just east of due north, past a detector at MP 65.3, where the speed limit is 40 mph, the 8,387 ft. siding at Giddings (MP 58.7, where the speed limit is 40 mph, to MP 56.8, where it is 65 mph), where CTC resumes, there is a flat crossing with the Austin Area Terminal Railroad (former Houston & Texas Central, later SP, line between Houston and Austin, now mostly abandoned), and an erstwhile San Antonio & Aransas Pass line to Waco once headed north (i.e. on the west side of the line), as the line to Hearne turns north-northeast again.
There is a jog to the north before the north-northeast heading is resumed, Loebau, a detector at MP 49.7, where the speed limit has risen to 70 mph, the 8,569 ft. siding at Dime Box (MP 45.9 - MP 44.1), Denaville, a detector at MP 39.1, and the 10,355 ft. siding at Caldwell (MP 33.0 - MP 31.0), with the west quadrant connector with the BNSF Galveston to Fort Worth line on the west side, the bridge carrying that line overhead, and the north quadrant connector trailing in on the west side at MP 31.5 within the siding, with speed limit 25 mph from MP 33.0 to MP 31.5, reverting to 70 mph at MP 31.0, as the line turns northeast, past a detector at MP 28.1, the 8,300 ft. siding at Cooks Point (MP 25.9 - MP 24.1), and a detector at MP 24.2.
The line turns just east of due north at a detector at MP 21.7, past a bridge over the Brazos River, the 8,606 ft. siding at Varisco (MP 18.9, where the speed limit is 65 mph, to MP 17.2, where it reverts to 70 mph), where a line east to Bryan once departed on the east side, a turn just west of due north, Mooring, a detector at MP 15.3, a flat crossing with the former MoPac line between Houston and Dallas (via Bryan) at Mumford (MP 11.6), where the speed limit has dropped to 60 mph, north of which that line runs alongside on the west side, as the line heads further west of due north, the 8,154 ft. siding at East Mumford (MP 10.7), a turn to the north, away from the former MoPac line just south of a detector at MP 5.2, and a turn northeast, past West Hearne (MP 2.4), where Yard Limits, ABS, start and the speed limit drops to 10 mph, to the wye junction with the UP Bryan sub. (the former Houston & Texas Central, later, SP, line between Houston and Corsicana/Dallas) at Hearne (MP 0.0), where there is a yard.