 The interior petroglyphs include an abstract shape, two curved lines, and a serpentine line with a pit at one end; two of the petroglyphs are filled in with ochre pigment, representing the only intact example of this painting technique in Illinois.The pictograph, which has deteriorated badly, depicts a human left hand; nearby flecks of paint from an unrecognizably faded figure likely indicate the site of the right hand.The paintings were likely added during the Late Woodland period, which lasted from 450 to 900 A.D.