The Historic Gillespie Dam Bridge spans the Gila River on Old U.S. 80 Highway between Arlington and Gila Bend and stands as an important work in Arizona and American transportation history. Arizona’s road system expanded after the Territorial Legislature created the Office of the Territorial Engineer in 1909 and, after statehood in 1912, a major east-west route across southern Arizona was surveyed between Clifton and Yuma. Early crossings of the Gila River along this route proved unreliable because of washouts and flooding, including a ford near Dome, a bridge at Antelope Hill in 1915, and a crossing below Gillespie Dam after the route was realigned in 1921. Automobiles often had to be pulled across the dam apron between 1922 and 1926, leading the Arizona Highway Department to design an all-weather bridge in 1925. Construction began in February 1926, and when the bridge opened to traffic on August 1, 1927, it became part of the southern transcontinental U.S. 80 and the national Ocean-to-Ocean Highway. Built by Lee Moor Construction of El Paso for $320,000, the 1,662-foot-long nine-span steel truss bridge was one of the longest bridges and the largest steel structure in Arizona at the time, using a more durable and flexible design than earlier reinforced concrete arch bridges. Its trusses and deep concrete supports were engineered to better withstand floodwaters. The bridge carried U.S. 80 traffic until 1956, when the route was shifted east to Rainbow Valley and this section was decommissioned as an interstate route, after which control passed to Maricopa County. It remains in local use and now also serves in regional and statewide bicycle plans. The nearby Gillespie Dam, built in 1921 by Frank Gillespie to supply water to Paloma Ranch, was then the largest privately financed concrete irrigation diversion dam in Arizona, replacing earlier dams at the site that floods had destroyed; it was itself breached in 1993 in one of the largest dam failures in Arizona history. The area also preserves remnants of the dam and bridge construction camp. Along the Gila River, rare riparian habitat supports rich plant and animal life, including cottonwoods, mesquites, willows, mallards, cliff swallows, great blue herons, bats, mule deer, javelina, and lowland leopard frogs, though such habitat in Arizona has declined from about 10 percent of the land before 1900 to less than 1 percent remaining intact today. Listed on the Arizona State and National Registers of Historic Places and recognized as a significant technological accomplishment in twentieth-century engineering, the bridge underwent a $7.3 million rehabilitation in the winter of 2011 as a 2012 Arizona Centennial Legacy Project, including structural repairs, replacement of original nonfunctioning roller bearings with modern pad bearings, roadway and approach improvements, and construction of a public plaza.