The geological significance of
Stone Mountain is more than just the exposed
granite, it's that the entire mountain is a granite
monolith -- literally, it's ONE huge
rock in the ground, 823
feet higher than the surrounding area at its peak. You can ride
cable cars up or down the
mountain, or you can
walk the side with a safely low
slope.
The entire area of Stone Mountain is set up as a Confederate history park on U.S. 78 east of Atlanta, Georgia, outside the Perimeter (Interstate 285). On the grounds, you can find small plaques inset into the ground dedicated to each Confederate state, listing its secession and re-admission dates -- except for two. Kentucky and Missouri each have a plaque, but only a secession date is listed; the legal governments of those states never formally seceded, but the numerous secessionists in those states formed extra-legal governments, supported by Confederate armies (which many of the secessionists joined), whose first act was to announce their secession from the United States. Since the official governments never seceded, those states were not forced to undergo Reconstruction or re-apply for admission to the Union after the war. (Those states also had stars on the Confederate "Southern Cross" battle flag.)
When I went to Stone Mountain 2 weeks before the 1996 Olympics, the highlight of the nightly laser show was the animation of the Davis/Lee/Jackson relief -- lasers outlined the actual carving, then drew legs onto the horses and made them appear to be running. (I know, it doesn't sound like much, but it looks pretty cool.)
The phrase "Stone Mountain" also has a colloquial descriptive meaning in the Deep South. To say that someone is "Stone Mountain" implies that he/she has deep, well-connected family roots in the area (a grandfather might have been a governor, a couple generations further back might have been a Confederate officer).