STORY: A large portion of the structure was destroyed before dawn on Wednesday when "unknown individuals detonated an explosive device," the Georgia Bureau of Investigation (GBI) said on its Twitter feed.
The collection of gray monoliths was erected in 1980 in the middle of a large field near the town of Elberton, Georgia, off Highway 77, and is listed as a tourist attraction by the state's travel site and the Elbert County Chamber of Commerce.
The GBI said the Elbert County Sheriff's Office, which has joined it and other agencies investigating the incident, discovered the damage when its officers responded to the blast.
Few additional details were provided, and it was left unclear whether authorities observed the explosion themselves or whether it was seen or heard by others and reported to police.
Aerial footage by ABC affiliate WSB-TV shows one of the structure's five monoliths crumbled into jagged pieces strewn about the ground, and a chunk of the monument's roof broken off at one corner. A large number of investigators and their vehicles were visible at the scene, about 100 miles (160.93 km) east of Georgia's capital.