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SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 146 
For the purpose of this summary, Mesoamerica can be divided into 
several cultural-geographical regions, especially evident beginning 
with the Regional Developmental Horizon. These are: The Central 
Plateau (Teotihuacanos, Xochicalcas, Toltecas, Mexicas, Cholulte- 
cas), the Gulf coast (Olmecas, Totonacas, Huaxtecos, Nonoualcas), 
the Oaxaca region (Zapotecas, Mixtecas), the Maya area (Chiapa- 
necos, Mayas, Quiches), western Mexico (Colimenses, Nayaritas, 
Coras, Tarascos), and a northern subregion that includes groups with 
Mesoamerican and North American influence (Casas Grandes, El 
Zape, La Ouemada, and others) . 
Finally, and for the purpose of constructing a cultural-chronologi- 
cal sequence, it is possible to recognize three principal horizons cor- 
responding to three stages, which in turn can be subdivided into 
evolutionary periods. This general scheme, based on the ideas of 
Olive (1958), is as follows: 
Primitive Horizon (Stage of Savagery) 11000-2000 B.C. 
Preagricultural Period 
Incipient Agricultural Period 
Formative Horizon (Stage of Barbarism) 2000-200 B.C. 
Village Formative Period 
Urban Formative Period 
Regional Developmental Horizon (Stage of Civilization) 200 b.c.-a.d. 1550 
Theocratic Period 
Militaristic Period 
PRIMITIVE HORIZON (11000 TO 2000 B.C.) 
Preagricultural Period (11000 to 6000 B.C.) — Paleoclimatic evi- 
dence permits the inference that the Valley of Mexico has been ex- 
posed to a series of alterations from wet to dry. Humid conditions 
prevailing during the terminal Pleistocene in the Valley of Mexico and 
the Valley of Puebla permitted the growth of pasture that supported 
the bison, horse, mammoth, and other large fauna, so that the early 
hunters encountered here conditions similar to those they had ex- 
ploited in North America. Their mobility, dictated in part by the 
animals on which they lived and in part by their own technology, 
brought about the dispersal of the early hunters through the Central 
Plateau, where projectile points of Clovis, Folsom, Plainview, and 
Lerma types identify their northern affiliation. 
The stone-artifact inventory, represented by projectile points, 
flakes, scrapers, knives, and other instruments related to hunting, 
coupled with evidence of the use of fire, the atlatl, and social or- 
ganization in small bands, suggests a very primitive level of cultural 
development during this period of early nomadic hunters. 
