The San Diego and Arizona Railway was a short line American railroad (AAR reporting marks SDA) founded by "sugar heir," developer, and entrepreneur John D. Spreckels, and dubbed "The Impossible Railroad" by many engineers of its day due to the immense logistical challenges involved. Established in part to provide San Diego with a direct transcontinetal rail link to the east by connecting with the Southern Pacific Railroad (which secretly provided the funding for the endeavor) lines in El Centro, California, the 148-mile (238-kilometer) route of the SD&A originated in San Diego, California and terminated in the Imperial County town of Calexico.
The company charter was executed on December 14, 1906, and the groundbreaking ceremony was held on the following September. Numerous delays (including government intervention during World War I) delayed the completion of the line to November 15, 1919. Damage to the lines from both natural disasters and sabotage exerted great financial pressure on the company, and in 1932 Spreckels' heirs sold their interests in the railroad to the Southern Pacific, which was theafter named the San Diego and Arizona Eastern Railway (SD&AE).