Obsidian artifact sourcing studies performed over the last 25 years have identified obsidian from outcrops around the communities of Zinapecuaro and Ucareo, Michoacan, at sites widely distributed in time and space. Recent data indicate that Zinapecuaro and Ucareo constitute distinct obsidian sources, although their proximity to each other and their similar chemical compositions merit their consideration as collectively comprising part of an obsidian source area. Sourcing studies that used Ucareo as well as Zinapecuaro source reference samples provide strong evidence of considerably greater pre-Hispanic utilization of the Ucareo source, and raise the possibility that at least some artifacts attributed to Zinapecuaro in studies that did not use Ucareo reference samples may be from the Ucareo source. These findings are supported by recent archaeological evidence of considerably greater exploitation of the Ucareo source, including what is probably one of the largest known pre-Hispanic quarries. Preliminary data provide a tentative chronology for settlement and exploitation of the source area.

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Survey and excavation conducted by Stoner and Nichols (2019) at Altica, located in the Basin of Mexico, recovered nearly 29,000 pieces of obsidian, most of which apparently came from the nearby Otumba source. Formal classification followed by attribute analysis revealed a number of distinct lithic industries represented in the collection, although most are represented by finished objects that do not appear to have been produced on site. Most of the material consists of flakes probably used as unmodified, informal tools and produced on expedient cores consisting of some nodules but mostly percussion blades, spent cores, and other artifacts recycled as secondary cores. I propose that Altica acquired its obsidian from workshops possibly located in an area where they apparently existed in later times and may have during the Early–Middle Formative, as well. Virtually all of the obsidian in the collection appears to have been used for domestic or subsistence activities and was not involved in production or exchange systems believed to have existed at that time. Two unusual caches containing macronodules provide some evidence to the contrary, suggesting that Altica may have been a transshipment center.

The site of Tula, Hidalgo, Mexico, is well known for its distinctive architecture and sculpture that came to light in excavations initiated some 70 years ago. Less well known is the extensive corpus of archaeological research conducted over the past several decades, revealing a city that at its height covered an area of c. 16 km 2 and incorporated a remarkably diverse landscape of hills, plains, alluvial valleys, and marsh. Its dense, urban character is evident in excavations at over 22 localities that uncovered complex arrangements of residential compounds whose nondurable architecture left relatively few surface traces. Evidence of craft production includes lithic and ceramic production loci in specific sectors of the ancient city. Tula possessed a large and densely settled hinterland that apparently encompassed the surrounding region, including most of the Basin of Mexico, and its area of direct influence appears to have extended to the north as far as San Luís Potosí. Tula is believed to have originated as the center of a regional state that consolidated various Coyotlatelco polities and probably remnants of a previous Teotihuacancontrolled settlement system. Its pre-Aztec history exhibits notable continuity in settlement, ceramics, and monumental art and architecture. The nature of the subsequent Aztec occupation supports ethnohistorical and other archaeological evidence that Tula's ruins were what the Aztecs called Tollan.

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For much of their history, prismatic blades were a relatively scarce item whose restricted occurrence suggested they functioned as prestige or luxury items. Some time prior to the Postclassic period, however, they became a widespread, ubiquitous, and mundane commodity in Mesoamerica, as indicated by ethnohistorical accounts as well as archaeological evidence. This occurred around the same time that blademakers began to prepare core platforms by pecking and grinding, a labor intensive process whose advantages are presumed to have played the primary role. The specific causal relationships involved, however, appear to pertain less to factors of increased productivity on the part of individual blademakers than to those of skill, as suggested by comparisons between core/blade technology used in areas close to obsidian sources and those used at sites further removed from the sources.But the truth is that they are cheap, and one doesn't mind using them up.-Torquemada (after Fletcher 1970) E-mail correspondence to: healan@tulane.edu 1 Kirchhoff did, however, mention "wooden swords with flint or obsidian chips along their edges," referring to the Aztec macuahuitl inset with obsidian prismatic blade segments.

This paper presents a method of identifying lithic reduction loci based on size-sorted debitage in the macroscopic size range. Multivariate analysis of decremental size classes of debitage derived from the use of nested screening provides a means of investigating the differential operation of size sorting at various size levels, so that size thresholds for distinguishing deposits of probable primary and secondary refuse can be identified on empirical grounds. The method is used to distinguish refuse dumps from what appear to be lithic reduction loci within an obsidian core/blade workshop excavated at the Early Postclassic city of Tula, Hidalgo, Mexico.

According to ethnohistoric sources, northeastern Michoacan became incorporated into the eastern frontier of the Tarascan empire during the mid-1400s. At that time, the region was multiethnic in character, with enclaves of foreigners living within communities as well as making up whole communities. Recent investigation in the Ucareo-Zinapecuaro source area uncovered evidence of an earlier foreign enclave consisting of two settlements in the Ucareo Valley whose ceramics are distinct from those of neighboring sites while indistinguishable from those of Epiclassic Huamango in the Acambay region of the Toluca Basin. The implications of these data alongside Ucareo obsidian exploitation and its role in the construction of the Protohistoric Tarascan-Aztec frontier are considered along with the results of preliminary chronometric dating.