The Omaha Road railroad established a station at Fort Snelling around 1870, but the railroad crossed the Minnesota River, not the Mississippi River. The Mississippi River crossing for trains was a few miles down river.
The first bridge built across the Mississippi at this location was the Fort Snelling High Bridge. It was a rickety iron wagon bridge. It was built on tall masonry piers, and was supported by a web of beams and cables. The wagon deck sat on top of this truss. This bridge was finished in 1880. It could not handle the load of trolley cars, so it was removed and replaced in 1909.
The photo above is a view of a structure that is believed to be the remains of the base of a support pier on the Fort Snelling side of the river. In addition to this pier support, part of the bridge abutment and retaining walls exist on the grounds of Fort Snelling.
The image below is a postcard depicting the Fort Snelling High Bridge. This image is based on a painting, so it is an idealized view of the scene.