Simplify the following text for a Grade 6 native English-speaking person.
Original: Both petroglyphs and pictographs can be parietal , meaning on the walls of a cave or rock shelter , open-air ( meaning they are made on exposed natural outcrops ) or monument-based which are made on stones consciously deposited .
Simplified: One can find petroglyphs and pictographs on the walls of a cave or on rock in open-air .