There are two related lines of Buchanans in Southwest Virginia during the early settlement period (1769-1780). Both lines originally settled in Old Chester County in Pennsylvania but had moved to Borden's Grant in Virginia by 1743. 
Children of James Buchanan. James died in 1763 in Old Augusta county. At least four of his children (Archibald, John, Robert, and George Buchanan), are believed to have moved south to Old Washington County in Virginia shortly after the area opened for settlement in 1769. Most of these children settled in the Locust Cove Creek area of Rich Valley, north of Saltville. This area would eventually become Smyth County. George, apparently settled further south in Washington County, as he appears on the Ebbing Springs Call signatory list, whose members mostly settled in the area south of Saltville.
Samuel Buchanan and children. At the same time Samuel, brother of James, moved to Old Washington County with his family. Samuel, his son samuel, Robert and John appear on the Ebbing Springs Call indicating that their presence in the area south of Saltville on the Middle and South Forks of the Holston. Moses Buchanan, believed by some to be another son also signed the Call, and lived in this area. Three Buchanan's, usually identified as sons of Samuel (Andrew, Mathew, and Moses) also appeared in Southwest Virignia about this time, though only Moses signed the call. . While these three Buchanans are commonly identified as sons of Samuel, Samuel did not mention them in his will. Nor are they mentioned by James in his will. It seems likely that they are close kin, but the exact relationship is unclear.
The following diagram shows the relationships and Of various records for these families in Washington County, arguably the most important is where five members of these two lines appear as signatories to the Ebbing Springs Call, as shown below: