Your are asking about the 3rd (U.S.) Tennessee Cavalry, much of which went to prisoner-of-war camps during the course of Forrest's raid. The garrison of Sulphur Springs Trestle, Ala., was attacked and captured on Sept. 25, 1864.
In his report, Maj. Gen. Forrest stated:
After a short parley with Col. J. B. Minnis, the commanding officer, who had expressed a desire for an interview, the fort surrendered. The enemy suffered severely in this assault. The colonel commanding was killed early in the fight. Almost every house was perforated with shell, and the dead lay thick along the works of the fort. The fruits of this victory consist, besides the prisoners, of 700 stand of small-arms, 2 pieces artillery, 3 ambulances, 16 wagons, 300 cavalry horses and equipments, medical, quartermaster's, and commissary stores. The trestle-work at this fort was 72 feet high and 300 feet long, and defended by two large block-houses, all of which were consumed by fire, and the prisoners turned over to Colonel Logwood, who started with them to the Tennessee River.
The service file of Lt. Col. Minnis is available through this message board. To do so, start with the link above, titled "Military Records Research Services".