The branch left the CSX (ex-Baltimore & Ohio) main at Georgetown Junction, near Silver Spring, MD. Some maps show a short segment of branch in operation near the main line; it might have lasted a few years there as there are warehouses and light industry near the old main line connection.
An auto club map shows the line extending all the way to the Maryland-D.C. border; this might have been for service to "Filter Plant Siding" indicated on the SPV atlas. In the atlas, the line is shown going from Georgetown Junction in Maryland to Chevy Chase, Bethesda, Dalecarlia Reservoir, into D.C. to "Filter Plant Siding", and into Georgetown.
The furthest end of the line paralleled the Chesapeake & Ohio canal into Georgetown. The years of construction and abandonment are not known, but the line was in service as recently as 1981, as it was used when the Smithsonian ran the "150th year anniversary" of the John Bull locomotive, the oldest operating steam locomotive still in existence.
The northern section of the line is now a paved trail called the "Georgetown Branch Trail". Further south, in the Bethesda area, the paved trail is known as the "Capital Crescent Trail". The line passes through deep cuts and has not been built on, but it is in a heavily built up area so there is a lot of car traffic.
The rails are still in place at the location of the Connecticut Ave (MD Route 185) crossing, as this street is probably too congested to close off for rail removal.