Gillespie Dam Highway Bridge, Steel truss bridge along Old US 80 Highway in Maricopa County, Arizona.

The Gillespie Dam Highway Bridge is a multiple-span steel Camelback through truss bridge over the Gila River in Maricopa County, Arizona. Its concrete piers and abutments reach 25 feet into bedrock, with the deepest pier 43 feet below the riverbed. Each truss section is 200 feet long, and the roadway was built to carry two 15-ton trucks at once.

This bridge was completed in 1927 and formed part of the original Route 80, a major transcontinental highway connecting the Pacific coast to the Atlantic. The route shifted away from this location in 1956 as transportation networks evolved.

The bridge carried U.S. Route 80, the transcontinental highway between San Diego and Tybee Island, from 1927 until 1956. In 2012 Maricopa County restored it for the Arizona Centennial and added an interpretive center; in 2018 it was folded into Historic US 80. Its name comes from Frank A. Gillespie, whose Gillespie Land and Irrigation Company built the dam it bypasses.

The bridge is accessible to visitors who want to explore this historical route, and an interpretive center on-site provides information about its history and engineering. Access is easiest from the nearby towns of Arlington or Gila Bend in either direction.

The bridge's Camelback truss sections were designed by engineer Ralph Hoffman with R. V. Leeson of the Topeka Bridge and Iron Works, after Arizona's concrete girder bridges kept washing out in desert floods. Each steel truss section is 200 feet (61 m) long, and the piers were sunk up to 43 feet (13 m) below the riverbed into solid bedrock.