Mystery Bridge Nr. 30: Little Bridge on the Prairie

Photos taken by the author in August 2013

I’m sure many of us have heard of and watched the TV series “Little House on the Prairie” while growing up. The same series that was based on the travels of Laura Ingalls Wilder, who was played by Melissa Gilbert, and also starred (the late) Michael Landon, who played Charles Ingalls, Laura’s father, and was involved in a great deal with directing and producing the show during its 10-year run, including the final movie in 1984, when Walnut Grove was blown to bits by the town’s people in retaliation to the railroad tycoon’s purchase of the community for his own use.

While it is unknown whether the real Walnut Grove (located in Redwood County, Minnesota east of Tracy) was actually blown up in reality, it is known that the community prides itself in the legacy of Laura, for it has a museum with a collection of artefacts from her days (Ms. Ingalls-Wilder lived for 90 years and wrote 10 books before passing on in 1957), and a dugout located two miles north of the community of 800 inhabitants, where the Ingalls family settled for several years- as mentioned in her book “On The Banks of Plum Creek.” The bridge shown in the photo above is located at the site of the dugout, spanning Plum Creek.

Now many people are wondering why a pedestrian bridge was chosen as a mystery bridge. The answer is simple: because of its unique design in comparison to the present-day mail-order truss bridges that have either a Pratt or bowstring arch design and are welded together at the company before being transported to the site. This pedestrian bridge is a bedstead Warren pony truss, but it is built using light steel, and whose diagonal beams are cylindral. Furthermore, unlike the truss spans whose connections are either pinned, riveted or welded, the connections on this bridge are very unusual for the diagonal beams are sandwiched together by opposite diagonal beams (with the floor beams sandwiching the outer diagonal beams) and held together by nuts and bolts. It is not 100% pinned-connected nor are the connections riveted. A close-up of the connections can be seen below and by clicking onto this link.

Close-up of the unusual connections as seen with the lower chord beam sandwiching a cylindrical diagonal beam.

It is unknown whether other pedestrian bridges have this unique feature, let alone when this bridge was built. But one variable is certain, which is the fact that this bridge was built prior to the creation of welded-truss bridges beginning in the 1980s. In other words, this bridge would have to be at least 40 years old, which if so, it has survived the test of time with little or no incident. While the flooring and railing look relatively new and thick in appearance, one can look more closely to see that the trusses support it, even though it is light weight and thin in appearance.

This leads to a couple questions involving this bridge:

1. When was this bridge constructed and who was the contractor?

2. Are there other bridges with such unusual connections like this one? If so, where?

3. Have you visited a Laura Ingalls Wilder site?

The third question should be on your 100 places to visit before dying list for Laura’s pioneer travels is part of American history which one should learn a bit about. Even the actors and actresses have stopped by Walnut Grove to learn more about Laura and take part in the annual pageant in July, including Karen Grassle (who played Laura’s mother Carolyn), Alison Arngrim (who played Nellie Oleson, Laura’s archrival) and Charlotte Stewart (who played Laura’s teacher, Ms. Beadle). There are seven historical sites that are devoted to Laura Ingalls Wilder, which apart from Walnut Grove include DeSmet (South Dakota), Spring Valley (Minnesota), Burr Oak (Iowa), Independence (Kansas), Pepin (Wisconsin), and Mansfield (Missouri). All of them are highly recommended to visit when passing through the midwestern part of the US as a tourist and as a person keen on knowing about American history.

Regardless of whether you are a civil engineer wanting to analyse this bridge or someone wanting to share a story of visiting the Laura Ingalls Wilder site, please share your thoughts on the three questions either by posting your comments here or on the Chronicles’ facebook or LinkedIn page as well as on James Baughn’s website. Or simply drop the author an e-mail at