English: The Southern Pacific Railroad, chartered in California in 1865 to build a railroad between San Francisco and San Diego, was purchased in 1868 by the group of California railroad investors known as "the Big Four" – Leland Stanford, Collis P. Huntington, Charles Crocker, and Mark Hopkins – who merged it with their Central Pacific in 1870. By 1877 the S. P. stretched eastward into Arizona. By 1878 Huntington also had heavy investments in the Texas-based Galveston, Harrisburg and San Antonio Railway and the Texas and New Orleans Railroad. By 1881 the S. P. had reached El Paso and had control of both these railroads, the Louisiana Western Railroad Extension Company, and Morgan's Louisiana and Texas Railroad and Steamship Company. In 1883 the Southern Pacific and its affiliates completed yet another transcontinental route in 1883, when the construction crews of the G. H. & S. A. and the S. P. met just west of the Pecos River. By 1900 the Southern Pacific and its affiliates owned more miles of track than any other line in Texas.

G. W. & C. B. Colton of New York constructed hundreds of important railroad-related maps in the mid- to late-nineteenth century, including this clear and simple map of the Southern Pacific, its affiliates, and their pending projects, ca. 1881.