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SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 146 
personalities of those few individuals sent by a contacting culture. 
Cultural modifications at each location would vary, but similar gen- 
eral shifts throughout the area might well be noted in studies of ar- 
chitecture, religious paraphernalia, land controls, farm production, 
population increases, and exploitation of raw materials. 
URBAN CENTERS IN A STATE OF RECONSOLIDATION, (a.D. 1200-1521) 
During the 1200's, certain shifts in the location of urban centers 
are noticeable. The Aztec ascendency certainly must have had an 
impact upon the northern frontier. Some of these centers might have 
ridden the political storm and held on to their home markets ; others 
may have cut themselves loose and developed their local areas to suit 
their own needs. Such adjustments can be noted in the cultural resi- 
dues from these centers after a.d. 1200. Multiplication in the number 
of archeological phases suggests rapid internal changes. The culture 
of the Hohokam in the Gila-Salt drainage at Snaketown shifted into 
the Classic Period and crystallized into a new material culture matrix. 
The shell center in the Altar Valley of northern Sonora apparently lost 
its market; while the urban center at Casas Grandes in Chihuahua 
was considerably changed and approached the very threshold of civil- 
ization. 
New lines of communication between Sinaloa and the North 
American southwest occur. There is an exchange of red wares, hand- 
modeled spindle whorls, overlap manos, and other items. The dis- 
tribution of the three-quarter groove axhead at this time appears to 
correlate with the area of the Macro-Nawan language group in west- 
ern Mexico. During this period a number of drastic events took place 
that helped to alter the history of the higher cultures of northern 
Mexico. Each center may have been affected by its own internal or 
domestic relationship with the native population surrounding it. It 
must be remembered that much of the area was still inhabited by 
primitive groups of the desert culture. The gathering of raw materials, 
food stuffs, and perhaps slaves may have led to poor public relation- 
ships with the indigenes. In addition, it has been suggested that cer- 
tain of the nomadic plains groups were penetrating the area at this 
period and that the balance of power established by the various trad- 
ing centers may have been put into jeopardy. 
The actual downfall may well have occurred after 1521 when the 
Spanish conquistadores entered Mexico and conquered the Aztecs. 
This destroyed (1) the market for certain goods held in esteem by 
the natives, but which were of no value to the Spaniard, (2) large 
blocks of native population by the introduction of two diseases — 
