Ila --
Most Confederate dead would have been buried by Federal soldiers who had no idea about identifying individuals or marking graves. Permanent markers were not placed for many, many years after the war. By that time all traces of most burials had long since vanished.
Here is a photograph taken in mid-May of 1864 near Spotsylvania Courthouse VA. On the right side of the picture can be seen a burial detail. Having collected the group of bodies seen in the foreground, they are about to bury this group of Confederate dead in a common grave --