Before refrigeration, salt was king (or at least royalty). One of the objectives for the Union forces was to disrupt salt production at Saltville, Virginia. The Confederates were anxious to protect it. The Federals were thwarted four times from their objective; the Confederates saved their salt until December 1864.
For the Confederates during the first Battle of Saltville in October, 1864, "It was thought at the time that the bravery exhibited in this contest by the reserves from Southwest Virginia was equal to the bravery exhibited by the citizens of this county at King's mountain in 1780." [Source]
The importance of salt was explained at Morton Salt site:
If the South had been able to protect its salt factories in Virginia and its salt deposits along the Louisiana gulf coast, the War between the States might have ended differently.
From the History of Salt:
Salt played a key role in the Civil War... . In December, 1864, Union forces made a forced march and fought a 36-hour battle to capture Saltville, Virginia, the site of an important salt processing plant thought essential to sustaining the South's beleaguered armies.
The History of Southwest Virginia, 1746-1786, Washington County, 1777-1870 has much more detail about troop movements (and the the text below).
Major General Burbridge [Union]...entered Virginia by way of Pikeville, Kentucky, and proceeded up the Big Sandy and crossed the mountains into Tazewell county at Richlands.
At the same time [Confederate] General Vaughan with his forces was ordered to Saltville from East Tennessee where he had until this time successfully opposed the advance of General Gillem's Brigade.