The branch to Grantsburg was built in the early 1880s. Trains were able to run to the Saint Croix River by 1883. The bridge was completed during 1883, but did not open until late in January of 1884. It departed the mainline at Rush City. The branch included 5-1/2 miles of track in Minnesota, then 10-3/4 miles of track in Wisconsin, plus the bridge over the Saint Croix River. The rail line was taken over by the Northern Pacific in 1900. Since this line was redundant with another NP route between the Twin Cities and Twin Ports, traffic dwindled and the line was eventually abandoned. The route is on the 1946 railroad maps, and was reported to still be standing in 1949, but it is gone from the 1951 map.
The only real information about this old bridge that I have seen so far is related to the #328 locomotive at the Minnesota Transportation Museum. It seems that this bridge was built very light. In fact, it was called spindly by railroad crews. It was so light that only the smallest of railroad engines could cross the structure. The NP kept an old 4-6-0 ‘Ten Wheeler’ in service long after that type was obsolete just to service the Grantsburg Branch. In fact, that is why #328 is one of the few ‘Ten Wheeler’ locomotives to have survived scrapping.
Another scrap of information is included in the book “Fifty Years In The Northwest” by William Henry Carman Folsom. He reports that when the rail line opened, over 1,000 people gathered for the event, 500 of which came in on the new railroad.
The photo above is looking east across the Saint Croix River. The embankment leading to the location where the bridge abutment was located is still visible. The photo below is looking upriver. The grassy ramp extending into the river is where the west abutment was located.