It was a railroad bridge that carried the CB&Q RR. The tracks crossed Illinois Rt 351 just off the south abutment of the current bridge. If you look east you will see a gravel road with a gate across it--that was the access road that paralleled the CB&Q RR tracks heading for the Illinois River RR lift bridge and was used by the bridge tender and maintenance crews. The tracks ran west from there and crossed the original US Rt 51 which is now the access road to the I&M Canal Lock 14 area. Those still visible piers were for the RR bridge that crossed the canal west of the original US Rt 51. They met up with the Rock Island RR tracks that still run east/west on the north side of the canal. Driving south on the original US Rt 51 you crossed the bridge over the Rock Island RR tracks; then the concrete structure over the canal; then under a steel beam structure on wood pilings that carried the CB&Q RR over the original US Rt 51. My dad remembered in the late 1940's when a truck driver delivering a full carrier of new cars tried to make it under that US Rt 51 RR bridge and created instant convertibles out of the cars on the top level of the carrier.
I thought these were for a road bridge due to the incline which the piers raise up. But it sure looks like its in the right location.
This is the same CB & Q railroad line that crossed the Illinois River on the lift bridge also on this site. Lift bridge was removed in 1980 so this one was probably removed around that time also.