Located just west of Big Stone City along US-12, this massive concrete arch is the largest arch bridge between Minneapolis and Aberdeen on this route.
Built in 1913-1914 during the line relocation and double tracking to cross the Whetstone River, the bridge features two absolutely massive concrete arch spans. At 60 feet long each, these are also likely the largest arch spans in the State of South Dakota on any railroad.
It was reported in Railway Review, Volume 26 that expansion joints were constructed into this bridge, partially because of the size of the arches, and also because issues with early cracking in other arches along the Milwaukee Road system. While expansion joints are common on roads and bridges today, the author has never seen such a thing in virtually any other concrete arch built for railroad use. An example of such a bridge with cracking in the spandrel walls (above the arch) can be seen near Gladwin, Iowa on the Kansas City line.
Image showing bridge soon after completion. Taken from Railway Review, Volume 26
The process of building this bridge was well documented through photos. Because this area was a lowlands, tons of fill was needed to raise the tracks and build the new alignment. This was accomplished through the use of temporary trestles and work trains. The work trains would then dump soil until the desired height was reached.
Once the fill was completed, the bridge construction began. It appears the footings and the arch rings were one pour, and then the rest of the bridge was done in other pours.
Minnesota Reflections has done a terrific job documenting the construction of this bridge. A photo showing the beginning of construction on the bridge can be seen here, while another photo showing the arches beginning to be formed can be seen here.
The original alignment was significantly lower than the current route, and it crossed the Whetstone River twice; once north of this bridge, and once near the Minnesota border.
Today, the arch is relatively secluded, and is best accessed from a large cliff along US-12. Unfortunately for the bridge, significant stabilization of the arches was needed at some time, leading to the metal bars that now help hold it up.
Overall, the arch appears to be in fair to poor condition. Cracks have begun to form in the arch, and it has needed bracing. The original expansion joints have largely done their job however, and can still be seen in the structure.
The author has ranked this bridge as being regionally significant, due to the large size, unique features and old age.
The photo above is an overview from the cliff along US-12.