Sierra Blanca, the county seat of Hudspeth County, is at the intersection of Ranch Road 1111, Interstate Highway 10, and U.S. Highway 80, eighty miles southeast of El Paso in the south central part of the county. It is also at the junction of the Southern Pacific and Missouri Pacific railroads. The town owes its existence to the competition that surrounded the construction of the nation's second transcontinental rail link. Collis P. Huntington's Southern Pacific line began building eastward from the Pacific in 1869, while Jay Gould's Texas and Pacific Railway began building westward from Central Texas in 1872. By November 25, 1881, the two crews had built to within ten miles of each other, and neither had any intention of yielding to the other. On the next day Huntington and Gould agreed to a compromise, and on December 15 Gould drove a silver spike to join the two roads seven miles southeast of Sierra Blanca Mountain. Transcontinental service began the next day. The town of Sierra Blanca, the site of the historic meeting, quickly grew into the most important commercial center in the area, providing stockyards and a railhead for local ranchers and serving as a shipping center for salt and other minerals. A post office opened in 1882 with James McFee as postmaster, but closed later that same year. In 1884 the population of the community was 126, and the next year the post office reopened. By 1892 the town had 200 inhabitants, two hotels, and a general store. Its population grew to 350 by 1914, when it also had a hotel, a news company, two general stores, and two cattle breeders. By the mid-1920s the town had 600 residents. During the late 1920s the population rose to an estimated 800, but it had dropped to 500 by the early 1930s, when thirty-two businesses were reported in Sierra Blanca. By the mid-1930s the population was estimated at 723, and by the late 1940s, at 850. It remained at 850 until the late 1960s, when it briefly rose to 900. It dropped again in the early 1970s to 600; by the mid-1970s the population was estimated at 700, and it was still reported at that level in 1990.
During the late 1980s Sierra Blanca had two churches and a school. A distinctive feature of Sierra Blanca is the fact that half the town goes by Mountain Time, under which the rest of Hudspeth County and El Paso County were placed by congressional legislation in 1921, while the other half goes by Central Time, as does the rest of Texas. In the mid-1950s the railroads and post office went by Central Time, but the county courthouse and schools used Mountain Time (as did the town's bars, so as to stay open later at night). In 1964 a waitress in a Sierra Blanca cafe told a visiting newspaperman that one tavern was supposedly closed down for a week because it opened in the morning on Central Time and closed at night on Mountain Time. In the early 1990s a waste-disposal company based in Oklahoma purchased more than 90,000 acres near Sierra Blanca, and in the summer of 1992 trains began arriving with treated sewage from New York City; an average of 225 tons a day was dumped there. In February 1992 the state of Texas selected Sierra Blanca as the site of a low-level radioactive-waste depository. Many area citizens were critical of the sludge dump and of the proposed radioactive-waste facility, citing the potential health hazards, and in the mid-1990s a local citizens' group was trying to fight the disposal projects. The population was 533 in 2000 with thirty-three businesses.