- The largest freight-hauling railroad in North America - Operates 8,300 locomotives over 32,200 miles of routes in 23 states - Major east-west route in southern Arizona - Tracks through Marana, Tucson, Sahuarita,Green Valley, Tubac, Rio Rico, Nogales, Benson, Dragoon, Willcox - The Southern Pacific Railroad (SP), nicknamed "Espee," was a major Class I railroad (1865–1996) that shaped the American West and Southwest (including southern Arizona), stretching from California to New Orleans ... the system was acquired by Union Pacific in 1996. Map