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SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 146 
correlation between material culture traits of the early Casas Grandes 
Convento and Pilon Phases and the Dos Cabezas-Pinaleno Phases 
in the San Simon village, the Georgetown- San Lorenzo Phases of 
Mogollon mountain culture and the Estrella- Sweetwater Phases of 
the Snaketown group. 
It was in this time block that the northern Mexican people, in the 
Casas Grandes area at least, are known to have drawn together in 
undefended villages located on high terraces near farmland. The 
simple houses generally surrounded a large ceremonial structure, with 
deep pits and inhumations scattered at random round the village 
premises. The lithic complement grew out of that of the previous 
phase. It would appear that these people, located along the southern 
border of northern Mexico, were culturally in advance of the more 
northerly societies owing to their proximity to the higher Meso- 
american hearth. Strong divergences between the north and the south 
become apparent in the material trait composition. Apparently, the 
population throughout the area was on the increase. Throughout this 
phase, more and more farmland was taken up by groups who decided 
to follow the soil-parasite trail, while an unknown percentage of the 
original stock retained their older nomadic desert-culture way of life. 
The latter left very little material residue to mark their existence, but 
may have figured as a social element in the play of the balance of 
power that must have been developing throughout northern Mexico 
at this time. 
URBAN AND CEREMONIAL CENTERS (a.D. 900-1200) 
The period from a.d. 900 to 1200 is one of the most intriguing 
phases of historical study in northern Mexico. The cultural picture 
remains much the same as in the preceding period, but along the east- 
ern and western sections of the Sierra Madre Occidental several 
large populations came into being. It should be noted that these cen- 
ters are in the area of the Macro-Nawan language group. Students 
have generally concluded that somehow these urban and ceremonial 
centers were inspired by the Tula-Mazapan Culture of Mesoamerica, 
believed to have had great control over all of Mexico at this time. It 
is assumed that merchants of the Tula-Mazapan Culture were estab- 
lishing trade relations in northern Mexico, as well as in southern 
Mexico, and that these contacts in the main were economically de- 
termined. Spinden (1928, p. 251) correlated this event in the his- 
torical continuum of northern Mexico with the Toltec trade items 
that appeared in the North American southwest in early Pueblo III 
times, around a.d. 1000 to 1200. Brand (1939, p. 105) postulated 
