No laws or even guidelines existed for state citizenship and the company a man joined. Most companies were centered on their home community, and the community was situated on a state line, such as West Point or State Line GA, members could come from both Alabama and Georgia. The same was true of this company.

Original members served under Capt Allen Lea as the "Lookout Rangers", a company assigned to Smith's 2nd Tennessee Cavalry.
http://www.tngenweb.org/civilwar/csacav/csasmith.html

Later several companies organized as the 11th Alabama Cavalry Battalion. Eventually enough companies from Alabama, Georgia and Tennessee were available to organize the 3rd Confederate Cavalry. After the "Lookout Rangers" reorganized at Whitesides TN, May 8, 1862, company officers were Capt Francis M Corn of Cedar Grove, Walker County GA, 1st Lt Benjamin Garrett of Broomtown Valley, Chattooga County GA, 2nd Lt John F Hogue of DeKalb County AL, and 2nd Lt William Thomas of Cedar Grove, Walker County GA.

Would you mind sharing your ancestor's name?

Whitesides can be seen near Raccoon Mountain in this map -