It appears the Pueblo people knew that someday the fractured rock face of Chaco Canyon that threatened the walls of Pueblo Bonito could collapse and cause damage and possibly even death.
For this reason they built a reinforcement for the slab. In 1941 the slab did indeed become dislodged from the Chaco Canyon wall, and a large section of the perimeter wall of Pueblo Bonito was damaged by the large pieces of falling rock.
Pueblo Bonito, Chaco Culture National Historic Park, New Mexico, USAChaco Culture National Historic Park, New Mexico, USA
Technical Information:
I photographed this photo with the digital SLR camera model Canon EOS-1Ds Mark III, aperture of f/11.0, exposure time of 1/25 sec. on ISO 100, as always I used a original Canon Lens, the focus lenght for this picture was 78mm.