<P> Stone Mountain was once owned by the Venable Brothers and was the site of the founding of the second Ku Klux Klan in 1915 . It was purchased by the State of Georgia in 1958 "as a memorial to the Confederacy ." Stone Mountain Park officially opened on April 14, 1965--100 years to the day after Lincoln's assassination . It is the most visited destination in the state of Georgia . </P> <P> Stone Mountain is more than 5 miles (8 km) in circumference at its base . The summit of the mountain can be reached by a walk - up trail on the west side of the mountain or by the Skyride aerial tram . </P> <P> Stone Mountain is a pluton, a type of igneous intrusion . Primarily composed of quartz monzonite, the dome of Stone Mountain was formed during the formation of the Blue Ridge Mountains around 300--350 million years ago (during the Carboniferous period), part of the Appalachian Mountains . It formed as a result of the upwelling of magma from within the Earth's crust . This magma solidified to form granite within the crust five to ten miles below the surface . </P> <P> The Stone Mountain pluton continues underground 9 miles (14 km) at its longest point into Gwinnett County . Numerous reference books and Georgia literature have dubbed Stone Mountain as "the largest exposed piece of granite in the world". This misconception is most likely a result of misrepresentation by granite companies and early park administration . Stone Mountain, though often called a pink granite dome, actually ranges in composition from quartz monzonite to granite and granodiorite . </P>

What type of geologic feature is stone mountain