I am sure that it was rebuilt by the Union after the fall of Little Rock in September 1863. It would have been a vital supply line from Deval's Bluff as most of the time the Lower Arkansas River was not passable due to low water to anything except shallow draft boats.

But before the fall of Little Rock there were a couple of reports in the OR's which suggested that the Ponchartrain was being refitted as an Ironclad Ram by using railroad rails for it armor. She already had a casemate of Oak 20 inches thick. There are a couple of letters by Union soldiers which support this, stating they watch the Gunboat burning in the Middle of the Arkansas River with it decks covered with railroad rails.

So the question is where did they get those rails if not from the railroad itself?