NO. I ARCHITECTURE OF PUEBLO BONITO — JUDD I9 



places capable of nourishing reeds and willows could have been 

 brought about, prior to erosion of the present arroyo, by only a slight 

 increase in annual precipitation. Perhaps echoing recollections heard 

 in boyhood, several of our elderly Navaho neighbors emphatically 

 insisted that Chaco Canyon was greener "before white men came," 

 that grass was then belly-high to a horse, and water could be had any- 

 where with a little digging. 



These geological opinions and these Navaho recollections lend 

 credence to the theory of climatic change in the Southwest, as advo- 

 cated by Huntington (1914) and others. Paucity of rainfall has long 

 been considered a principal cause of arroyo formation in the South- 

 west, and Douglass (1935, p. 49), with his tree rings before him, 

 sees a succession of droughts down through the years. There was a 

 short one about A.D. 920; another, around 980; still another, more 

 severe and more widespread, between 1090 and 1101, Of our 59 

 datable timbers from Pueblo Bonito only two were cut during that 

 decade ; only six were felled during the 40-year period of subnormal 

 rainfall, 1005-1044. 



"In the 500-year history of Oraibi even the small droughts were 

 accompanied by reduced building" (Douglass, 1932, p. 312). 

 Throughout the long advance of Pueblo civilization, house construc- 

 tion always declined in times of reduced rainfall (Mindeleff, 1891). 

 Timbers from old Hopi villages and trees from Arizona forests show 

 that periods of below-average precipitation recurred irregularly dur- 

 ing the 10th, 11th, and 12th centuries but Pueblo Bonito had been 

 deserted 100 years or more when the Great Drought of 1276-1299 

 caused far-reaching devastation throughout the Plateau Province and, 

 presumably, hastened abandonment of the famous cliff-dwellings of 

 Mesa Verde National Park. 



The prehistoric arroyo. — In 1924 and 1925 Dr. Kirk Bryan, a 

 geologist with the U. S. Geological Survey and an acknowledged 

 authority on groundwater resources of the Southwest, undertook in 

 our behalf a study of sedimentation and erosion in Chaco Canyon. 

 He examined minutely the banks of the present arroyo, of post-1850 

 origin, and learned much previously unsuspected of Chaco Canyon 

 history. He discovered dead campfires and bits of broken pottery 

 20 feet and more below the surface ; he noted that relics of Pueblo III 

 peoples, the builders of Pueblo Bonito and its kind, occurred in the 

 upper 4 feet only and those of earlier peoples below that level. 



Bryan learned that the main Chaco Canyon fill had been built up 

 over the centuries by intermittent flood waters that shifted from place 



