Minneopa Creek Stone Arch

Located just west of Mankato, this stone arch carries County Road 69 and the Union Pacific Railroad across Minneopa Creek. The first bridge at this location was a tall timber pile trestle, which crossed the deep Minneopa Creek valley. In 1879, the railroad desired to reduce curves in the area, and slightly realigned the railroad. As part of this work, a 20-foot stone arch was constructed, at a width of 187 feet. The remainder of the trestle was filled with earth embankment, a typical practice for this era. This section used a traditional design, including a semicircular arch and wing walls which extended diagonally from the bridge. A keystone on the bridge indicates that this portion of the bridge was completed on March 24, 1879. C. Strom constructed the arch using limestone quarried at Kasota, Minnesota; and the bridge was designed by T.P. Greer, Chief Engineer of the St. Paul & Sioux City Railway.

Due to the maintenance issues presented by the two curves at this location, it was decided to realign the tracks in 1905 as part of a larger improvement project between St. Paul and Sioux City. As a result, a new 20-foot stone arch with a width of 400 feet was completed just north of the original structure. This arch also would use semicircular design, but due to the angle at which it crossed underneath the railroad, this section would use only one angled wing wall on either end, with the other wing walls placed parallel to the railroad. James McClure completed the new bridge, using stone quarried at his Kasota quarry. After completion of the new structure, the old structure would be abandoned. After abandonment of the original alignment, the right-of-way was sold to Blue Earth County for use as a road. The roadway later became Trunk Highway 5, which became part of US Highway 169 in the 1920s.

In 1924, the bridge received a major reconstruction, which connected the two separate structures with a new 95-foot curved concrete arch. As a result, the north wing walls of the 1879 structure and the south wing walls of the 1905 structure would be removed. In addition, a concrete lining would be added to the base of the walls, and a concrete floor poured through the structure. The center portion was careful to match the existing dimensions of the bridge, and would be heavily reinforced to compensate for the sharp bend in the structure. These modifications give the bridge its current appearance, and its current width of 682 feet. In the 1930s, the roadway would be relocated north, placing it over the 1905 section of the bridge.

Stone arch bridges were commonly used by American railroads, due to the durability. However, exceptionally wide structures like this are uncommon. Due to deteriorating condition, the bridge was rehabilitated in 2017, with new concrete added to the interior walls. Previous inspections indicate that the northern (active railroad) portion of the bridge was in extremely poor condition at the time of rehabilitation. Overall, the bridge appears to be in fair to good condition, with the repairs holding up well. The author has ranked this bridge as being moderately significant, due to the unique situation in which a common design was used.