﻿136 SMITIISONIAX .MlSCEI.l-ANEUUS CUl. LECTIONS \()I.. 74 



In addition to the purely archeological phase of the expedition, 

 geophysical investigations were undertaken in an effort to trace cli- 

 matic or other changes which may have taken place in I'haco Canyon 

 since the occupancy of prehistoric Pueblo Bonito. Three test pits 

 near the ruin, each more than 12 feet in depth, provided stratigraphic 

 sections of the valley fill in addition to that already available in the 

 arroyo. From the evidence disclosed in these pits, and elsewhere, it 

 now appears that Pueblo Bonito was originally constructed on a slight 

 elevation, superficial indications of which have since been entirely ob- 

 literated through building up of the level valley floor by means of 

 blown sand and silty deposits washed in from the sides of the canyon. 

 These deposits vary in depth from 2 to 6 feet and frequently contain 

 scattered objects of human origin. 



A pre-Pueblo ruin, the existence of which was disclosed only 

 through caving of the arroyo bank. afl:'ords further evidence of the 

 human occupancy of Chaco Canyon at a consideral)le period prior 

 to the erection of Pueblo Bonito and the other major ruins, a similar 

 structure having been excavated by the National Geographic Society's 

 Reconnaissance Expedition of 1920. This ancient habitation consisted 

 of a circular pit 12 feet 9 inches (3.9 m. ) in diameter and about 4 

 feet (1.2 m.) deep, excavated in the former valley floor; its roof 

 was qf reeds and earth supported l\v small poles which reached from 

 the wall of the excavation to upright posts placed just within an 

 encircling bench. A considerable quantity of potsherds, collected both 

 from the deliris which fllled the ])it and from the masses of adobe 

 which had fallen awav from the bank. estal)lishe(l tb.e period tn which 

 the dwelling belongs as " early black-on-white."" a culture well known 

 throughout the San Juan drainage. Idie fact that the floor of this 

 ancient structure lay 12 feet below the present valle\- surface is evi- 

 dence not only of the vast amount of silt which has been deposited 

 since occupancy of the room. Ijut carries the [jromise. also, that other 

 similar lodges may \ et be disclosed by excavation or through the 

 gradual erosion of the valley. 



A topographical survey of that ])art of Chaco Canyon adjacent to 

 Pueblo Bonito. completed ]i\- the i()22 ex])edition. aflords the hrst 

 accurate map of the ])rinci])al ])ortion of the C haco C anxon Xalional 

 ]\Ionument. This sur\f\- correctly locates nine of the major ruins 

 and indicates the relati\e i)osition of most, but not all. of the smaller 

 structures to be fonnd. es])eciall\' ihnsf along the southern side n\ 

 the can\'on. 



