Spanning the South Platte River, the Rainbow Arch Bridge carried vehicular traffic from its completion in 1923 until its closure in 1988. Engineer James B. Marsh of Des Moines, Iowa, designed the structure in 1922, and Denver bridge contractor Charles G. Sheely built it in 1922-23 for just over $69,000. With its eleven 90-foot concrete arches, the bridge extended over 1,100 feet, and a year after it was finished, light standards were installed that linked it visually with Fort Morgan's Main Street. For the bridge, Marsh used a design he had patented in 1912, an ingenious blend of steel and concrete technologies that combined the concrete arch form with a sophisticated steel reinforcing system so heavy and complex that his bridges have been called steel structures with concrete veneers. Marsh built several small-scale and medium-scale rainbow arches throughout the Midwest in the 1910s, and the Fort Morgan bridge represented the first large-scale application of his distinctive design. Listed on the National Register of Historic Places, it is the only rainbow arch built in Colorado, and at its completion it was the longest rainbow arch in the world. It remains a nationally significant example of this important but relatively uncommon structural type and symbolizes the permanence of early highway construction in the state.