But that is not the area that I am referring to. This was a straight track which passed under Washington Street where the present right Wilson Bridge approach on I-495 is today. If you face the river the old cemetary will be on your left. I had worked in this area since the early 70's and never saw any traces of rail facilities between the old Ford motor plant and Jones Point. Track from the Wilkes Street section entered the Ford Plant. I never saw anything down river from that. There are many old foundations and dry dock walls present.
My 1943 USGS topo map of the Washington area shows what appears to be an industrial spur of the Southern running south from Wilkes St. to Hunting Creek, with a siding into a large building on the waterfront about midway along it -- your Ford plant, I assume. At this time there didn't appear to be any industry south of this plant, so the balance of the line most likely was just used as a tail track for switching the plant.
I then dug out my 1929 topo of the same area and see that the spur existed then and, in fact, extended farther west along Hunting Creek to serve something right on the shore a short distance east of the US Rt. 1 bridge (a sewage plant?), crossing (with a connecting track) the Mt. Vernon interurban line. The Ford plant (?) wasn't there then, but at that time there was some facility on Jones Point served by multiple sidings. I have no info on when the line was built or dismantled, but maybe the Southern group has come to your rescue on that.
As long as we're dissecting historic Alexandria rail lines, I should throw in this tidbit: The original line between Alexandria and Washington -- the Alexandria & Washington RR -- followed the east side of the Washington Turnpike (now US 1), entering Alexandria itself on St. Asaph St. and terminating at a passenger station located on the north side of Princess St. between St. Asaph and Pitt Sts. Before the Civil War there was no connection between the A&W and the two other railroads entering the city. But when the military took over the A&W, it built a connection to the Orange & Alexandria which shows on the 1885 (date correct?) topo. The PRR moved in after the war and by the early 1870s had absorbed the A&W and built the A&F to Quantico to connect with the RF&P. When it did, it built a line parallel to the one built by the USMRRs through the center of Alexandria and relocated the passenger station to Cameron St.
The freight and passenger stations of the W&OD's predecessor (originally the Alexandria, Loudoun & Hampshire) were located on the north side of Princess St. east of Fairfax St. The passenger station, which also originally housed the company offices, was demolished in the 1930s, I think, but the brick freight station survived into the 1950s.