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The Southern Pacific built east from Los Angeles reaching Yuma in September 1877, Casa Grande in May 1879, Tucson in March 1880, and El Paso in May 1881. The Buffalo Bayou & Colorado Railroad began building west from Houston before the Civil War. After the war it was reorganized as the Galveston, Harrisburg, & San Antonio and began building west again in 1870. It reached San Antonio in February 1877, then in May 1881 built west to meet the SP. The SP continued building east out of El Paso under the charter of the GH&SA in a race to cut off Jay Gould's Texas & Pacific. The SP under Huntington reached Sierra Blanca on November 25, 1881 while the T&P was just ten miles to the east. The next day Huntington and Gould met in New York and signed an agreement whereby the Texas and Pacific agreed not to build west of El Paso and the SP granted the Texas and Pacific trackage rights between Sierra Blanca and El Paso. The last spike on the Sunset Route in Texas was driven on January 12, 1883 about three and a half miles southwest of the present Pecos River bridge on a portion of line abandoned during 1892.
The GH&SA came under SP control in 1885 and was absorbed into the Texas & New Orleans in 1927. The T&NO was absorbed into the SP in 1961. The addition of automatic block signals to the Sunset Route across west Texas was completed in 1926. There were train order stations at El Paso, Sierra Blanca, Valentine, Marfa, Alpine, Marathon, Sanderson, Dryden, Langtry, Del Rio, Spofford, Uvalde, Sabinal, Hondo, Lacoste, San Antonio, Seguin, Luling, Harwood, Flatonia, Glidden, Eagle Lake, Tower 17 in Rosenberg, Eureka, Houston Tower 87 in Englewood Yard, Dayton, Devers, Beaumont, Orange, Echo, Lake Charles, Jennings, Midland, Crowley, Rayne, Lafayette, Baldwin, Morgan City, Schriever, Raceland Junction, and Avondale Yard in New Orleans.
CTC was installed in short segments near major terminals in the 40s and 50s and were generally controlled from nearby train order stations or interlocking towers. The first segment outside a major terminal was from Paisano to Alpine in 1930. The next segment was from El Paso to Sierra Blanca in 1959. The T&P helped pay for part of that project. In 1973 the SP began installing CTC at Flatonia working its way west and completed the project in 1974. For reference, I've added a timetable for the Valentine Subdivision.