I looked at his CMSR and the organization existed prior to Ralston leaving the 6th Georgia Cavalry. If you look closer, he is dropped from the rolls of the 6th Georgia Cavalry per Special Order Number 119/6, 23 May 1864.

This UNKNOWN organization was made up of absentees and others and a company sized element was formed around March-May 1864. It was apparently initially organized by a couple of 39th Georgia absentees and grew until Ralston was elected its commander. The organization is mentioned in Volume 49, Part 1, page 963 of the Official Records.

The UNKNOWN organization is some type of militia, reserves, or other type of organization that remains a mystery at the moment who authorized (if anyone, Joe Brown, local officials) their organization and if they were ever officially brought under Confederate national government control.

Respectfully,

Gerald D. Hodge, Jr.
War Between the States Historian
Historian: 39th Georgia Volunteer Infantry
http://39thgavolinfrgt.homestead.com/39thHomepage.html