Petroglyphs carved onto rock surface by prehistoric Native American(s)..
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Lost Civilizations: 12 Societies that Vanished in Mystery - WebEcoist
Why would a flourishing civilization, advanced for its time, suddenly cease to exist, its inhabitants gone and its architecture abandoned? Conspiracy theorists offer all manner of offbeat explanations including alien abduction, but in the case of these 12 societies, the causes were likely more mundane: natural