Southern Emigrant Trail, also known as the Gila Trail, the Kearny Trail, Southern Trail and the Butterfield Stage Trail, was a major land route for immigration into California from the eastern United States that followed the Santa Fe Trail to New Mexico during the California Gold Rush. Unlike the more northern routes, pioneer wagons could travel year round, mountain passes not being blocked by snows; however, it had the disadvantage of summer heat and lack of water in the desert regions through which it passed in New Mexico Territory and the Colorado Desert of California. Subsequently, it was a route of travel and commerce between the eastern United States and California. Many herds of cattle and sheep were driven along this route and it was followed by the San Antonio-San Diego Mail Line in 1857–1858 and then the Butterfield Overland Mail from 1858 to 1861.

Butterfield Overland Mail was a stagecoach service in the United States operating from 1858 to 1861. It carried passengers and U.S. Mail from two eastern termini, Memphis, Tennessee, and St. Louis, Missouri, to San Francisco, California. The routes from each eastern terminus met at Fort Smith, Arkansas, and then continued through Indian Territory (Oklahoma), Texas, New Mexico, Arizona, Mexico, and California ending in San Francisco. On March 3, 1857, Congress authorized the U.S. postmaster general, at that time Aaron V. Brown, to contract for delivery of the U.S. mail from St. Louis to San Francisco. Prior to this, U.S. Mail bound for the Far West had been delivered by the San Antonio and San Diego Mail Line since June 1857.