﻿NO. I SMITHSONIAN EXPLORATIONS, I925 Sj 



occurred throughout the entire period of human occupancy. Hearths 

 were encountered eight feet, and more, below the surface ; evidence 

 of frequent reconstruction, of aherations in the grouping of dwel- 

 Hngs, of destructive conflagrations were disclosed by these cross 

 sections. 



In addition, a former channel for the diversion of flood waters — 

 mud-laden floods that refused to stay within the man-made banks 

 intended for them — to cultivated fields below the village was brought 

 to light for the first time since abandonment of Pueblo Bonito a 

 thousand years or more ago. No trace of small irrigation ditches has 

 yet been found in Chaco Canyon and the diversion channel just 

 mentioned tends, therefore, to confirm the opinion of the Expedi- 

 tion's stafl:" and technical advisers that the ancient Bonitians practiced 

 a system of flood irrigation not unlike that employed today by certain 

 of the more successful Navaho farmers of northwestern New Mexico 

 or, on a larger scale, by the Hopi, Pima and Papago Indians of 

 Arizona. 



During the course of the National Geographic Society's explora- 

 tions at Pueblo Bonito and Pueblo del Arroyo, indisputal^le evi- 

 dence of the former presence of human beings, semi-sedentary in 

 habit, has been observed as much as 20 feet below the present 

 valley surface. These ancient folk were far less civilized than the 

 Bonitians but, owing to the depth at which their infrequent remains 

 lie buried, we may not hope to learn nnich al)out them. Fragmentary 

 remains are there but the limits of the crude culture to which 

 they belong are still indeterminable. 



There are factors that point to certain changes in the geophysical 

 appearance of Chaco Canyon since the period of Pueblo Bonito's 

 greatest prestige ; there is accumulative evidence in support of pos- 

 sible climatic changes during or since that same period. The former 

 existence of a prehistoric arroyo, 18 feet deep immediately in front 

 of Pueblo Bonito, was finally established by the Expedition of 

 1925. The data already assembled suggest that this ancient water 

 course, now completely filled and leveled over, may have rendered 

 the cultivated fields of the Bonitians unproductive, thus forcing 

 abandonment of this, at one time the most influential and power- 

 ful of all prehistoric pueblos in the southwestern United States. 



