The Galveston, Harrisburg, and San Antonio Railway Company was chartered on February 11, 1850, as the Buffalo Bayou, Brazos, and Colorado Railway Company. It was the first operating railroad in Texas and the second railroad west of the Mississippi River. General Sidney Sherman established the line, a hero of the Battle of San Jacinto, in 1847 purchased from the Harrisburg Town Company the unused town lots previously allocated to the failed Harrisburg and Brazos Railroad. The “Colorado” in its name does not refer to the state but rather to the Colorado River of Texas. Obtaining northern investors, Sherman organized the company in June 1850, and surveying began the following year near Buffalo Bayou. The following year, the first locomotive, the General Sherman, was received, and the first track was laid. By August 1853, 23 miles had been completed from Harrisburg to Stafford Point. The line reached Richmond on the Brazos River in 1855, Eagle Lake in 1859, and Alleyton in 1860, completing 80 miles between Harrisburg and Alleyton.
The Civil War stopped construction, and the line failed with the financial collapse of Texas during Reconstruction. In 1868, it changed owners and became the Galveston, Harrisburg, & San Antonio Railroad. More tracks were laid towards San Antonio, and the new owners also constructed the first telegraphs along the route. After reaching San Antonio, the road continued to El Paso, where it met the Southern Pacific Railroad, ensuring the line’s transcontinental route would use the southern portion of Texas rather than the north.
The railroad used the nickname Sunset Route, a name in general use by 1874 and later adopted by the Southern Pacific Railroad for the entire line between New Orleans, Louisiana, and Los Angeles, California. As early as 1878, the railroad reached an agreement with the Southern Pacific Railroad regarding the expansion of the Galveston, Harrisburg, and San Antonio west of San Antonio. The two companies met up in January 1883 with a silver spike driven just west of the Pecos River to mark the completion of a new transcontinental route across Texas. The line continued to expand to various cities over the next several decades.
Between March 1, 1885, and June 30, 1889, the Galveston, Harrisburg, and San Antonio were leased to the Southern Pacific Company. Before and after that period, the company was operated by its organization until March 1, 1927, when it was leased to the Texas and New Orleans Railroad Company. It was merged into the latter company on June 30, 1934. Texas and New Orleans lasted until November 1, 1961, when it was merged into the Southern Pacific Railroad. Today, it is the oldest component of the Southern Pacific system.