"The South Third Avenue bridge in Marshalltown is one of fifteen known concrete rainbow arch bridges in Iowa. It is considered an important structural form in the development of reinforced concrete technology and illustrates Iowa's significant civil engineering heritage. It was designed by the March Engineering Company of Des Moines, Iowa, for the City of Marshalltown. James B. Marsh also was granted the U.S. patent for this bridge style. Also considered important is the fact that the interior reinforcing varies from that specified in the original patent and, in some details, varies from the design plans.
"This [HAER] documentation fulfills the obligations the Iowa Department of Transportation and the Federal Highway Administration under a Memorandum of Agreement between the Federal Highway Administration, the Iowa State Historic Officer, and the Advisory Council on Historic Preservation, pursuant to 36 CFR 800. The bridge was photographed in November, 1979, by Grau Studios, Marshalltown, Iowa and printed by Demett, Muessig, and Associates, Ltd., Iowa City, Iowa, in February, 1981."