The sub extends northward 20 miles from Baldwin, Florida, where the Jacksonville Terminal Subdivision's S Line and Florida Gulf & Atlantic Railroad meet just north of Baldwin Yard, a classification yard.
According to Jacksonville Division Timetable Number 4 published in 2005,[1] the sub runs from milepost SM 0.18 to milepost SM 20.0, where it joins the Nahunta Subdivision, a former Atlantic Coast Line Railroad, in Callahan, Florida.
The sub has three direct traffic control blocks (DTC), double tracks on its full entire route and two defect detector locations over its length.
The sub crosses the Norfolk Southern Railway at milepost SM 15.5.
In 1980, the Seaboard Coast Line's parent company merged with the Chessie System, creating the CSX Corporation.