Question: What Virginian explorer passed through an area near the Clinch River?

Context paragraphs:
Thomas Walker (explorer): Thomas Walker (January 25, 1715 – November 9, 1794) was a distinguished physician and explorer from Virginia; in the mid-18th century, he was part of an expedition to the region beyond the Allegheny Mountains and the unsettled area of British North America.  Walker and fellow Virginian, Indian agent, explorer for Patrick Henry, legislator of three states, surveyor of KY/VA & TN/NC borders, and later Revolutionary war general, Joseph Martin, were some of the first colonialists to travel in this area.  Martin's son, Revolutionary War officer Col. William Martin, describes the naming of the area and river in a letter to historian Lyman Draper,

Flanary Archeological Site: Flanary Archeological Site is a historic archaeological site located near Dungannon in Scott County, Virginia, United States.  Located across the Clinch River from Dungannon, the site was inhabited as early as 6000 BC and remained in periodic use into the Woodland period, with occupation potentially continuing until c. AD 1600.  The terminus ad quem for occupation is 1750, when Thomas Walker's expedition passed through the area and found no Indian villages.  Excavations conducted in 1977 in preparation for the construction of a bridge revealed that the village site, featuring posthole patterns indicating a palisade surrounding the village, lay primarily south of the bridge in the vicinity of a 1764 log cabin.

Kingston Fossil Plant coal fly ash slurry spill: The TVA Kingston Fossil Plant coal fly ash slurry spill occurred just before 1 a.m. on Monday December 22, 2008, when an ash dike ruptured at an 84 acre solid waste containment area at the Tennessee Valley Authority's Kingston Fossil Plant in Roane County, Tennessee.  1.1 e9USgal of coal fly ash slurry was released.  The coal-fired power plant, located across the Clinch River from the city of Kingston, uses ponds to dewater the fly ash, a byproduct of coal combustion, which is then stored in wet form in dredge cells.  The slurry (a mixture of fly ash and water) traveled across the Emory River and its Swan Pond embayment, on to the opposite shore, covering up to 300 acre of the surrounding land, damaging homes and flowing up and down stream in nearby waterways such as the Emory River and Clinch River (tributaries of the Tennessee River).  It was the largest fly ash release in United States history.

Guest River: The Guest River is a short tributary of the Clinch River in southwestern Virginia in the United States.  It is part of the watershed of the Mississippi River by way of the Clinch, Tennessee and Ohio Rivers.  According to the Geographic Names Information System, the river has also been known historically as the Guests River.

Longhunter: A longhunter (or long hunter) was an 18th-century explorer and hunter who made expeditions into the American frontier wilderness for as much as six months at a time.  Historian Emory Hamilton asserts that "The Long Hunter was peculiar to Southwest Virginia only, and nowhere else on any frontier did such hunts ever originate" although the term has been used loosely to describe any unofficial American explorer of the period.  Most long hunts started in the Holston River Valley near Chilhowie, Virginia.  The hunters came from there and the adjacent valley of the Clinch River, where they were land owners or residents.  The parties of two or three men (and rarely more) usually started their hunts in October and ended toward the end of March or early in April.

Poplar Creek (Tennessee): Poplar Creek is a tributary of the Clinch River in Anderson and Roane counties in East Tennessee.  Draining a watershed area of more than 82 mi2 , it enters the Clinch near the former K-25 site, a short distance downstream from the confluence of East Fork Poplar Creek, its largest tributary.

Powell Mountain: Powell Mountain (or "Powells Mountain") is a mountain ridge of the Ridge-and-valley Appalachians of the Appalachian Mountains.  It is a long and narrow ridge, running northeast to southwest, from about Norton, Virginia to near Tazewell, Tennessee.  It separates the Clinch River basin and the Powell River basin of Powell Valley.  It was named for an 18th-century explorer.

North Fork Clinch River: The North Fork Clinch River is a river in the U.S. states of Virginia and Tennessee.  It rises along the slopes of Wallen Ridge in Lee County, Virginia, and empties into the Clinch River at Hancock County, Tennessee, just across the Tennessee/Virginia state line.

Beaver Creek (Tennessee): Beaver Creek is a tributary of the Clinch River in Knox County in East Tennessee.  It drains a watershed area of 86.5 mi2 between Copper Ridge and Black Oak Ridge.  It flows from northeast to southwest from the Gibbs High School area, through the Halls, Powell, Karns, Solway, and Hardin Valley communities, entering the Clinch downstream from Solway.

Clinch Mountain: Clinch Mountain is a mountain ridge in the U.S. states of Tennessee and Virginia, lying in the ridge-and-valley section of the Appalachian Mountains.  From its southern terminus at Signal Point peak, which lies at the intersection of Knox, Union and Grainger counties near Blaine, Tennessee, it runs in a generally east-northeasterly direction to Garden Mountain near Burke's Garden, Virginia.  It separates the Clinch River basin, to the north, and the Holston River basin, to the south.

Supporting paragraphs: Flanary Archeological Site Thomas Walker (explorer)
Answer: Thomas Walker