Bridge L4770 on Township Road 213 over Mahoney Creek
Bridge number: L4770
Year built: ca. 1915
Span length: 10 feet, 4 inches
Length of arch barrel: 20 feet, 6 inches
Adapted from the National Register of Historic Places nomination form prepared by Jeffrey A. Hess. Bridge No. L-4770 was listed on the National Register of Historic Places in 1989.
Bridge No. L-4770, located in a rural area of Fillmore County about 2 miles east of Fountain, is a single-span, stone-arch bridge that carries Township Road 213 over Mahoney Creek. Built of gray coursed-rubble limestone, the bridge displays a nearly semicircular arch (10-foot span, 4-foot rise) springing about 7 feet above grade from well-defined impost ledges that extend outward from the intrados about 6 inches. The bridge's limestone matches the area's bedrock, but the quarry site has not been identified. In comparison to similar bridges in Fillmore County, the structure's masonry is precisely cut and laid. Ring stones are rectangular and uniform, measuring about 6 inches in width and 12 inches in height. The bridge's corner stones are sharply squared and masonry joints range from about one-half-inch to 1-inch thick. The spandrel walls are recessed by one course from the flared wing walls. As is common with country stone-arches throughout southeastern Minnesota, the intrados is coated with a thin cement sheath showing formwork impressions from the original centering. The bridge's overall width is 20 feet, 6 inches. On both elevations, the bridge is surmounted by a concrete parapet with angle-iron posts that have lost their rails. The parapets appear to be additions. However, they do not affect the bridge's most significant elements, which are the design of the impost ledges and the configuration of the arch itself. The bridge's masonry, especially the sharply cut corners and distinct coursing, is much more precise than that of other Fillmore County stone-arch bridges.
Bridge No. L-4770 is historically significant for the engineering embodied in its design and construction. With its short-span, nearly semi-circular arch and distinctive, 6-inch-wide impost ledges, the bridge displays the essential features of a standard stone-arch design that appears to have been developed by the Minnesota State Highway Commission during the second decade of the 20th century for use in rural areas of southeastern Minnesota. Bridge No. L-4770 is the only surviving example of the design in Fillmore County and one of the few unaltered examples in the state.
The Minnesota State Highway Commission was officially organized in 1905 to improve the quality of roads and bridges in the state. To fulfill its responsibilities, the commission assigned field engineers to assist county governments with highway projects and prepared a series of standard bridge plans, including plans for beam spans, plate, girders, low trusses and high trusses, reinforced concrete slab and girder spans. Although the commission's reports do not mention a stone-arch plan, the field engineers apparently had at their disposal a standard short-span design appropriate for the limestone region of southeastern Minnesota. In 1912, J.J. Davy, the commission's engineer for Fillmore County, supervised the construction of a 12-foot stone arch in the county. Although the structure's design is unknown, another bridge, similar in design, was constructed in Houston County in 1915.
Bridge No. L-4770 survives in relatively unaltered condition. Its most notable features are a semicircular arch and well-defined, 6-inch-wide impost ledges, which probably served as supports for the arch centering. These same features are replicated on a nearby bridge in Houston County (Bridge No. L-4009) and two bridges in Wabasha County (Bridge No. L-1122, Bridge No. 93741). The construction history of Bridge No. L-4770 is unknown. County records do not mention the structure and township records are missing. The existence of the similar "impost-ledge" structures in Houston and Wabasha counties, however, implies that the bridge is an example of a standard, Minnesota State Highway Commission stone-arch plan. Considering that the commission's plan was implemented in Houston County in 1915, a construction date of 1915 is plausible for the bridge. Bridge No. L-4770 remains the only intact example of the state-sponsored design outside of Houston County.