question: How long is the extension of the blue ridge mountain range that Nichol's Gap Road was built over?
answer: 70 mi
context: Title: Nichol's Gap Road
  Passage: The Nichol's Gap Road was a central Pennsylvania highway established in the 18th century near Maryland extending westward from the Black's Gap Road "just west of Little Conewago Creek" at the "Crofs Keys" stand of James Black.  The road was past both the Rock Creek Church and 1761 Samuel Gettys tavern where Gettysburg would be surveyed in 1786.  The highway was built over the South Mountain (Maryland and Pennsylvania) via Nichol's Gap ( ) and down the Devils Racecourse into the Cumberland Valley, allowing access to the 1762 Hagerstown, Maryland.  Called the "Hagerstown Road" during the Battle of Gettysburg, parts of the road are now designated (east-to-west): U. S. Route 30 in Pennsylvania, Pennsylvania Route 116 (Fairfield Road to Fairfield, Pennsylvania), Iron Springs Road, Gum Springs Road, and Old Route 16 (the summit section through Nichol's Gap--"Fairfield Gap" during the American Civil War—no longer has a roadway.)
  Title: South Mountain (Maryland and Pennsylvania)
  Passage: South Mountain is the northern extension of the Blue Ridge Mountain range in 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.  The Appalachian National Scenic Trail follows the crest of the mountain through Maryland and a portion of Pennsylvania.
  Title: Paris Mountain
  Passage: Paris Mountain is a peak of Blue Ridge Mountain on the border of Loudoun County and Clarke County in Virginia.  The 1926 ft peak, which is located just north of Ashby's Gap and the town of Paris, for which it is named, represents the highest elevation in both counties.  The peak is accessible by Blue Ridge Mountain Road from the gap.  The Appalachian Trail is crosses the western slope of the peak.
  Title: Mountain City, Georgia
  Passage: Mountain City is an incorporated town in Rabun County, Georgia, United States.  The population was 829 at the 2000 census.  The town straddles the Eastern Continental Divide in a deep gap in the Blue Ridge Mountain front.  The gap allows U.S. Route 441 to cross the range at an elevation of 2168 feet without the significant grade required by roadways at most other mountain passes along the Georgia Blue Ridge.
  Title: Keyes Gap
  Passage: Keyes Gap or Keyes' Gap is a wind gap in the Blue Ridge Mountain on the border of Loudoun County, Virginia and Jefferson County, West Virginia.  The gap is traversed by Virginia State Route 9/West Virginia Route 9.  The Appalachian Trail also crosses the gap.
  Title: Blue Ridge Mountains
  Passage: The Blue Ridge Mountains are a physiographic province of the larger Appalachian Mountains range.  This province consists of northern and southern physiographic regions, which divide near the Roanoke River gap.  The mountain range is located in the eastern United States, starting at its southernmost portion in Georgia, then ending northward in Pennsylvania.  To the west of the Blue Ridge, between it and the bulk of the Appalachians, lies the Great Appalachian Valley, bordered on the west by the Ridge and Valley province of the Appalachian range.
citations: Nichol's Gap Road South Mountain (Maryland and Pennsylvania)