Hell's Half Acre is an area of exposed rocks and boulders in a clearing near Hot Springs, Arkansas.
In the 1870s there was a hotel nearby and guests would walk a trail to see the site, often referred to as a "bottomless pit".
It was long theorized to be an extinct volcano, however there is no volcanic activity in the area.
Also, the rocks themselves are not volcanic but a form of chert common to the Ouachita Mountains.
Based on a large amount of preforms, blanks, and rejected cores found near the site it is now theorized this may be an ancient Native American quarry.