A majority of the gravel roads that are within a 100 mile round trip (by bicycle) of Atlanta are probably going to be gone within the next 10-15 years. Just too much value in the land to not pave the roads to up the selling price as sprawl keeps sprawlin'. It's a shame, we lost a good one - Brushy Mountain road - last year and another road a couple years before that. All told probably only 8-12 miles but that's almost half of the total gravel out Dallas (GA) way. No way to forestall it, the city, property owners and so forth aren't interested in keeping it country, as it were.
Regardless there's enough gravel within a 2 hour drive of the city to keep anyone busy for years - right now it's just getting the routes developed but I've been working on that myself as is TimothyH with his website. Hopefully within a year or two they're be another 5-600 miles of turn-key routes in play.