I had suspected that this was a possible location. Thanks for doing the research and getting confirmation.
This bridge is surely long gone, but I can't help but wonder if there might be some crumbling remains of the stone pylons hiding in the trees.
I looked at several old atlases 1885,1902,1919. The bridge was located on South 9th Street where it crosses Doyle Creek.(39.1900N,96.0799W) The creek is the old Kansas River channel. The river made a major course change between 1902 and 1919.
The bridge in the photo has masonry piers, but there also appears to be a pair of lally columns in the river directly south of St. Mary's. Any info/pictures of a St. Mary's bridge that sat on lallies?
I was under the impression that there was a Bowstring bridge over the Kansas River at St. Mary's. The Kansas River, I believe, may have changed courses since then so it might be a bit difficult to say exactly where the bridge was. I am glad to see a photo of it however.
The Kansas River has a history of changing courses even in relatively recent years. This is readily apparent at Manhattan where the Ashland vicinity Kansas River Bridge on Rosencutter Road (abandoned and private) is now on dry land.