Where to Mountain Bike near Atlanta?

One of our readers posted the following message and we would appreciate any recommendations. "I am looking for some good mountain biking around the northern part of Atlanta. I have biked a ton at Sope Creek, but, am looking for some variety. I would like to find a new place that has some beginner and intermediate trails. Does anyone have any suggestions?" I haven't had much time to research other areas (this whole work thing gets in the way), but I did find a lot of videos of people mountain biking at Ft. Yargo in Winder, GA (a short drive up 85 or 316). I've also heard that there is a trail that follows the Little River near Woodstock or maybe Kennesaw. You Tube also had a helmet cam video of Sope Creek that looked pretty cool, but nowhere near as funny as this video.