The line was extended in 1779 and 1780 to the point at which it would first cross the Cumberland River. From there, the state of Virginia hired Thomas Walker to survey the line to the Mississippi River. Walker did not do a perfect job due to dense virgin forest, mountainous terrain, and rough riverbeds. In 1821 the state of Tennessee did a survey of the line to determine its true border with Kentucky, but this was not resolved since Kentucky was not participating. A joint survey by the two states was conducted in 1859, commanded by Austin P. Cox and Benjamin Pebbles. They started a survey from the New Madrid Bend of the Mississippi River to the Cumberland Gap, placing a stone slab every .