RailVet-sorry I've missed this post until now.
As far as the last revenue freight to/from Pope's Creek-I don't know. However, I do know that the last customer at the Pope's Creek end of the line was a company called the "Pope's Creek Salvage Company". They were in the business of scrapping ships anchored at Pope's Creek. The scrap steel was loaded into gondolas and shipped to the Bethlehem Steel plant at Sparrow's Point (Baltimore). A steam crane, which had been converted to diesel power was still at Pope's Creek in the early 1970's. Whether it was moved out by rail or scrapped on the spot I have no idea.
In March of this year a number of our informal "Pope's Creek Railfans" group hiked the old roadbed from Pope's Creek to Route 301. One of the big suprises was a trestle, approximately two miles in from Pope's Creek road, about 50 feet long and 40 feet above the water of Pope's Creek at its highest point. One of the group had actually ridden that fan trip from Alexandria, VA to Pope's Creek and return-the date was 1955, IIRC. He said the trip consisted of about 6 PRR coaches with two E units for power. The wye at Pope's Creek, where locomotives were turned, can still be made out.
According to the booklet
Baltimore and Potomac, The Pope's Creek Branch written by Charles County historian John Wearmouth, printed in 1986, PEPCO built the Morgantown Generating Station in the late 1960's with the plant going on line in 1970. Originally built to primarily burn oil (brought in by barge at Morgantown), the oil crisis of 1973 triggered a conversion to coal in 1973. (80% oil/20% coal at the time of construction.)
The line from Faulkner to Pope's Creek was scrapped in the early 1970's by the Lagenfelder Construction Company, the same company that scrapped the Washington, Brandywine and Point Lookout Railroad that ran from Brandywine to the Patuxent River Naval Base.
The line was extended from Faulkner to Morgantown in the late 1960's to facilitate construction of the power plant. The point where the railroad owned track ends and the power plant trackage begins is in Faulkner, not too far south of the Red Top Liquor store at the Route 301/Pope's Creek Road intersection. There is a small sign lettered "Pope" at trackside. The last 7.5 miles of track, from Faulkner to the generating station, is owned and maintained by the power company. This is known as the "Morgantown Industrial Track".
Coal was originally trucked to the plant with the 1973 conversion to coal as the primary fuel used necessitating the shipment of coal by rail. (A former neighbor of mine, who lived in Newburg at the time of the extension of the Pope's Creek sub, told me that the deep cut in Newburg disrupted the flow of a number of shallow wells in the area, including that of his parents' home.)
For more information on the Pope's Creek sub, check out:
http://www.traingod.railfan.net
Check out the "Historic Photos".
Here's a photo from September 1968 of the power plant under construction:
http://www.traingod.railfan.net/CK/PC-Morgantown.jpg
The Pope's Creek depot, still standing in July 1967:
http://www.traingod.railfan.net/CK/PC-PCfrtDep.jpg
Finally, a photo of the pier area, with a couple of cranes and lots of scrap metal lying around, looking like a war zone, also from July 1967:
http://www.traingod.railfan.net/CK/PC-PopeTerm1.jpg
The brick building in the background is the original SMECO (Southern Maryland Electric COoperative) generating plant, which was in operation from 1938-1953. The hulk of this building still stands.
I'll query the group and see if I can come up with a date of the last revenue freight movement.