PEWKES] RELATION OF COMPOUNDS TO PUEBLOS Lay ¢ 
that they form two distinct architectural types—the true pueblos and 
the compounds—differing radically from each other. These indicate 
two centers of cultural distribution, one of which was in the east, the 
other in the south, or, broadly speaking, in what is now called Colo- 
rado and New Mexico on the one hand, and southern Arizona on the 
other. Between these centers lies the great valley of the Little Colo- 
rado, which was a meeting ground of prehistoric people, wherein a 
mixed cultural type was formed and distributed. It has a composite 
type of pottery showing features of the Colorado-New Mexican and the 
southern Arizonian ware, sometimes one, sometimes the other, pre- 
dominating. 
The aboriginal migrations of man in the Southwest may be roughly 
likened to the spread of vegetation or to the stocking of regions by 
animals from a-center of distribution. There was a slow passing of 
clans from one place to another, largely influenced by the scarcity or 
abundance of water and food. The pressure of incoming hostiles 
played a part in determining the directions of the migrations, but not 
the most important part, the main cause being failure of water, due 
to desiccation of the land, and increased salinity. The situation of 
streams was an important factor in these migrations, as it determined 
the location of the trails which man followed. The routes of the pre- 
historic migrations are indicated by ruins left along the banks of these 
streams. In these movements sites that could be readily defended 
were generally adopted, but each group of clans acted independently: 
there was little unity of action and at times open hostility among 
members of the same group. Clusters of clans were continually 
uniting and groups of families were as constantly diverging from the 
main body. Two great movements can be detected, one setting from 
the Rio Grande toward the west and south, and the other from the 
Gila toward the north and east. An objective region for both was 
the valley of the Little Colorado, which offered an attractive home 
for all the tribes. 
The Grand Canyon of the Colorado, situated north and west of the 
Pueblo region, served to keep back from the Little Colorado Valley 
the inhabitants of the country in those directions, so the immigrants 
entered this region in prehistoric times mainly from the east and 
south. One stream of colonists followed down the San Juan, another 
went up the northern tributaries of the Salt. The ruins at Black 
Falls mark the southern limit of the people passing west and south 
from the San Juan; those on the Little Colorado above Black Falls 
can be traced to the southern colonists. 
The advent of the southern colonists into the Little Colorado Basin 
was at alate day; their influence was widely spread. The tributaries 
entering the Salt from the north served as pathways by which the 
culture of the south spread from the Gila north and northeast. 
