480 BUREAU OF AMERICAN ETHNOLOGY [Bull. 194 



what later Schultz site on the Sheyenne River southwest of Fargo, 

 N. Dak., have not been reported for locales upstream from the Arz- 

 berger site until one reaches the traditional homeland of the Hidatsa 

 north of the Square Buttes in sites which my older Hidatsa informants 

 identify as those they occupied before moving to the mouth of the 

 Knife River. 



This mass migration into the Missouri VaUey of South Dakota 

 seems to have come about as a consequence of an extensive drought 

 in the central plains which occurred about A.D. 1450. It resulted in 

 the displacement of many of the original inhabitants, the realinement 

 of populations, and the introduction of many new cultural traits 

 which produced local cultures now identified as belonging to the Chou- 

 teau or Slope Aspect. In South Dakota, there was a northward move- 

 ment from the western tributaries of the Missouri River in Nebraska 

 of the ancestral Arikara. There occurred simultaneously an east- 

 ward movement, along the tributaries of the Missouri River in South 

 Dakota, of the ancestors of the southern Mandan who had already 

 changed considerably both linguistically and culturally from those 

 who had long lived on the Missouri. As our knowledge of the arche- 

 ology of the sites of the Chouteau Tradition or Aspect grows, it is 

 becoming increasingly evident, however, that a majority of these 

 sites represents the various branches of the ancestral Arikara. 



These newcomers to the Northern Missouri Valley introduced: A 

 new house type, square to roughly circular in outline with the four- 

 post support for the roof and weak peripheral wall posts; distinctive 

 incised-decorated pottery designs; a high regard for catlinite; simple 

 fortifications with or without bastions, which evolved to simple en- 

 circling ditches ; distinctive flaking tools cut from the edges of buffalo 

 vertebrae; and other tools from bone. A few cultural differences 

 between these earliest sites suggest that regional differences probably 

 already existed. 



When these two populations of agriculturalists came together, 

 there followed widespread cultural borrowing between those belonging 

 to the Missouri Valley Aspect and those of the Chouteau or Slope 

 Aspect. The most significant change for the people of the Missouri 

 Valley Aspect was the adoption of the four-post roof support to a 

 small square lodge with rounded corners by those who had formerly 

 built large rectangular lodges. Those peoples of this tradition, living 

 chiefly upstream from the Grand River, soon modified these small 

 four-post lodges by the addition of rather heavy forked peripheral 

 posts usually 12 to 13 in number, and 6-7 feet high, against which 

 they leaned wooden slabs set back 5-6 feet to form a distinctive 

 feature which in later years the Historic Hidatsa referred to as the 

 atvMsh area. The southern groups downstream from the Cannonball 



