K carrier route that probably was a segement on some sort of Philadelphia to Washington, D.C. route. Modern fiber markers seems to follow the same route (if not identical ROW) from Wilmington to Baltimore #2 on their way to Washington, D.C. This fiber/route is what became AT&T first fiber optic route stretching from Cambridge, MA to Washington, D.C. and went live in 1983.
There is an older brick style lightguide hut in Elkton proper and a Bell central office facility with a corner stone of 1958. However, its not positive if the Bell office is the same Elkton refered to on AT&T route maps. After all this route probably went in in the mid-1930s, almost 30 years before the construction of the current Elkton CO. Still its a possible start pending further information.