The way it's phrased can make it sound like accidental, but there are a large number of such sites all across the southwest. The largest involve very, very big

The way it's phrased can make it sound like accidental, but there are a large number of such sites all across the southwest. The largest involve very, very big boulders and extensive human modifications. Given the cultural importance and how obvious the production process is, it's likely many or most were intentional.