Straddling the North Carolina/Tennessee border in the Southern Appalachians, Great Smoky boasts the largest stands of old-growth forest in the eastern United States and the greatest biodiversity of any U.S. park. This yields a fall outburst of reds, yellows, purples, browns, and golds rivaling those of the New England countryside.
The colors generally peak in mid- to late October at higher elevations (which have a climate similar to New England's), but can start as early as mid-September with the turning of "early" trees like yellow birch, American beech, mountain maple, hobblebush, and pin cherry.
At lower and middle elevations, where the color tends to be most spectacular, the blend includes such beauties as sugar maple, scarlet oak, sweetgum, red maple, and hickory. East-west trending Highway 441 (Newfound Gap Road) gets the bulk of the leaf peeping traffic, which is typically quite heavy (especially on weekends), but the Clingmans Dome Road and the Cades Cove Loop are very popular as well.
For something different, take the Roaring Fork Motor Nature Trail, a narrow, steep, winding (but paved) one-way road that passes through color-rich forests and offers glimpses of Roaring Fork Creek as a bonus. Try to visit on a weekday or before 10:00 a.m.
The park website has links to webcams showing the progression of fall color that sweeps through the Smokies.
Always check for road conditions before visiting this park. October is a transitional month that can bring foul weather and road closings on short notice. By late October, the park begins reducing visitor center hours and closing some facilities and secondary roads for the winter.