The postcard's label says, "Largest Cement Road Bridge in Northwestern Missouri, near Sheridan."
BH Photo #107962
From the above article the bridge was built in 1911 and the location is on State Highway B at (40.507808,-94.546050).
I may wrong but I think MDot raised the grade on Highway B to match Highway 46 to the north and covered most of the bridge which might still be in place. It would be worth a road trip to check out.