The Rockpile (also known as Elliot Combat Base) is a solitary karst rock outcropping north of Route 9 and south of the former Vietnamese Demilitarized  one (DMZ). Its relatively inaccessible location, reached only by helicopter, made it an important United States Army and Marine Corps observation post and artillery base from 1966 to 1969. This 230 metre high limestone outcrop served as a US observation post for directing artillery to targets across the DMZ and into Laos.