Question: How long is the extension of the blue ridge mountain range that Nichol's Gap Road was built over?
Sentence (from "South Mountain (Maryland and Pennsylvania)"): From the Potomac River near Knoxville, Maryland, in the south, to Dillsburg, Pennsylvania, in the north, the 70 mi range separates the Hagerstown and Cumberland valleys from the Piedmont regions of the two states.
Relevant evidence: Yes