This may shed some light on the "Rock City Guard.
"The Rock City Guard was pre war militia organization called the Rock City Guards of Nashville Tennessee, see http://www.first-tennessee.co.uk/articles/rockcityguards.htm.
The guards were mobilized at the onset of the war in 1861 and became the first Tennessee Infantry. A short history of the regiment follows; The 1st Tennessee originally consisted of ten companies
Company A - The Rock City Guards
Company F - The Railroad Boys
Company B - The Rock City Guards
Company G - The Brown Guards
Company C - The Rock City Guards
Company H - The Maury Greys
Company D - The Williamson Greys
Company I - The Rutherford Rifles
Company E - The Tennessee Riflemen
Company K - The Martin Guards Organized May 9, 1861 at Nashville, Tennessee; mustered into service August 1, 1861.
The regiment first went into camp at Allisonia, Franklin County, which they named Camp Harris in honor of Governer Isham G. Harris. It soon moved to Camp Cheatham where it received instruction in drill and tactics. On July 10, 1861, it was ordered to Virginia and as a brigade, the regiment took part in the Cheat Mountain Campaign in West Virginia.
On February 17, 1862, they were ordered to the west to serve in the forces which later came to be called The Army of Tennessee. The 1st Tennessee fought at Shiloh and Corinth and arrived at Harrodsburg, Kentucky on October 6, 1862.
The regiment suffered heavy casualties in the Battle of Perryville on October 8, 1862, losing more than half of its men in killed, wounded, and missing.
As part of General Bragg's army retreated into Tennessee, reaching Murfreesboro in November, 1862, it was again heavily engaged at the Battle of Murfreesboro, December 31, 1862. It remained in camp around Shelbyville till July, 1863, when the army retreated to Chattanooga. There was little activity until the Battle of Chickamauga, September 18 - 20, 1863, where the regiment did valiant service.
The regiment also participated in the Battle of Missionary Ridge and helped cover the retreat to Dalton, Georgia, which it reached November 27, 1863.
In February, 1864, again in Cheatham's Division, the regiment was ordered to Mississippi to reinforce General Leonidas Polk, but after reaching Demopolis, Alabama it was returned to Dalton, Georgia.
At Resaca, Georgia, May 16, Maney's Brigade was attached to General A.P. Stewart's Division, but was in Cheatham's Division again on the 17th at Adairsville, Georgia. It held the famous "Dead Angle" in the Battle of Kennesaw Mountain June 27.
Just prior to the Battle of Peachtree Creek, General Johnston was relieved of his command of the army and was replaced by General John B. Hood. With the army's defeat at Jonesboro on August 29th, Atlanta’s fate was sealed, and Hood ordered the evacuation of the Army of Tennessee. The evacuation was completed on September 2, 1864. Hood’s forces retreated through Lovejoy’s Station, and into rural Georgia. The regiment went with Hood back to Tennessee, taking part in the Battles of Franklin and Nashville, in November and December, 1864. After the defeat in Nashville, the army fell back across the Tennessee River, and the regiment halted at West Point, Mississippi for a short while.
The last battle was the Battle of Bentonville in North Carolina and after the battle the regiment was surrendered by General Joe Johnston on April 26, 1865. The 1st Tennessee was paroled at Greensboro, North Carolina May 1, 1865. Out of nearly 1200 men on the rolls of the 1st Tennessee, only 125 officers and men were left at the final surrender.