|Robert Thompson posted|
Some comments ask where this was. But there is no answer.
My first thought was that a high river level pushed it off the abutment. But it looks like that field on the other side of the river is well below the underside of the bridge. My next theory was that the bridge abutment was made of stones and some stones under the left side got eroded away; the bridge started to fall; but the rails "caught it." But if that was the case, then the top stone should still be held to the bottom of the footing by the bolts we see. My current theory is that the stones were limestone instead of dolostone, and the top stone deteriorated until it cracked and crumbled away.
Update: Another theory is tornado damage.