A rather nice recitle of the May 10, 1864 event is found in

Bluegrass Confederate, The Headquarters Diary of Edward O Guerrant,
edited by William C. Davis & Meredith L. Swentor,
LSU Press, Baton Rouge, 1999, pp.431-36

"Four miles from Wytheville the Enemy were stopped by Jones' Brig. Which occupied the Gap of the Cove . . .

Battle of Cove Gap near Wytheville, VA. 10 May 1864 between Conf. forces under BG J. H. Morgan & Fed. forces
under Gen. Averill

. . . We lost some 30 men, killed and wounded. . . "

Rocky Gap is mentioned as "two miles to the left", but not further identified.

OR Atlas Plate shows Cove Mt. approximately 7 miles North of Wytheville, Rocky Gap ~ 20 miles.