If you're hunting for the national park with the most vibrant fall foliage, Great Smoky Mountains National Park, straddling the Tennessee and North Carolina border, makes the strongest case. The park is home to roughly 100 different tree species, and because they don't all turn at the same time, the mountainsides fill with an overlapping mix of reds, oranges and yellows rather than a single wave of color. As autumn progresses, the color literally rolls down the mountainsides from the highest elevations toward the valleys, stretching the display into one of the longest leaf seasons in the country.