If I remember right, after he made it out of Selma, he made his way back north to Plantersville and then turned west from there. He captured the hospital at Plantersville immediately after the fight at Selma and paroled the doctors and badly wounded.

I don't know the exact location of the crossing, but assume he followed one of the roads west from the Plantersville/Ebenezer Church area and hit the Cahaba west of that point. It couldn't have been too far north, because he was back down at old Cahawba to meet with Wilson a short time later.

Dale