NOTES ON OBSIDIAN SOURCES OF THE SOUTHERN …members.peak.org/~obsidian/pdf/darling_1993.pdf · NOTES ON OBSIDIAN SOURCES OF THE SOUTHERN SIERRA MADRE OCCIDENTAL ... (Pires-Ferreira

Ancient Mesoumericu, 4 (1993), 245-253 Copyright © 1993 Cambridge University Press. Printed in the U.S.A.

NOTES ON OBSIDIAN SOURCES OF THE SOUTHERN SIERRA MADRE OCCIDENTAL

J. Andrew Darling Museum of Anthropology, University of Michigan, Ann Arbor, Ml 48109, USA

Abstract

Recent fieldwork has identified a previously unknown obsidian source area in southern Zacatccas and northern Jalisco. Evidence of prehistoric use of surface gravel and nodule outcrops in the Huitzila-La Lobera source area includes raw­material extraction and the production of cores, large blade blanks, rough bifaces, and other artifacts. Unusual variability in color is characteristic of the sources and includes a banded variety described as "rainbow" obsidian. Characteristics of this source area are compared to the Llano Grande obsidian source area in Durango. Implications for understanding the distribution of obsidian from sources in the Sierra Madre Occidental to the cultures of the north Mcsoamerican frontier are presented and discussed.

Few naturally occurring materials have contributed to our knowledge of past societies as much as obsidian or volcanic glass. This is particularly true of Mesoamerican obsidian for which there is abundant literature concerning sources, procure­ment , tool production, and trade. Understandably, the geo­graphic focus of this work has centered on sources that supplied Mesoamerican heartland areas including those in the neovolca­nic zones of the central highlands of Mexico and in Guatemala. Of particular importance are the numerous volcanic-glass sources distributed throughout the famous Trans-Mexican belt of Plio-Pleistocene volcanoes encompassing the majority of well-known obsidian sources in northern Mesoamerica. From cast to west these include among others the Hidalgo sources such as Sierra de Pachuca, sources in Queretaro including Fuentzuelas and El Paraiso, Ucareo and Zinapecuaro in Michoacan, and finally in Jalisco sources in the vicinity of the Tequila volcano including Tequila, Magdalena, and Teuchitlan (Pires-Ferreira 1975; Vogt et al. 1990).

Recent research in the Sierra Madre Occidental has identi­fied a series of previously undocumented obsidian sources. These sources are of specific importance to understanding ob­sidian procurement, utilization, and exchange among the vari­ous cultural systems located in the northern frontier region of Mesoamerica. The following discussion will describe these sources and briefly discuss their importance to the archaeology of the northern zone.

OBSIDIAN SOURCES OF THE SIERRA MADRE OCCIDENTAL

The Sierra Madre Occidental is a physiographic province formed by an immense volcanic field extending from Chihua­hua in the north more than 1,200 km to the south where it is partially buried by the deposits of the Trans-Mexican Neovol-

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canic Belt. The Sierra Madre is formed by two extensive igne­ous sequences dating to the Tertiary period; the first from 100 to 45 million years ago buried by a second group dating from 34 to 23 million years ago. The upper volcanic supcrgroup con­sists predominantly of rhyolitic ash-flow tuffs and silicic lava and constitutes one of the world's largest expanses of silicic vol­canic rocks (Albritton 1958; McDowell and Clabaugh J 979; McDowell and Keizer 1977; Moran-Zenteno 1990; Swanson ct al. 1978). Within these upper mid-Tertiary deposits at least two separate sources of volcanic glass have been identified. These include the Llano Grande/ Cerro Navajas source and the Huitzila-La Lobera source described here (Figure 1). Sources in far northern Mexico that are not considered in the following dis­cussion include, in Sonora, La Sierra de Pinacate, identified by Pastrana (1990), and sources north of Janos, Chihuahua (P. C. Weigand, personal communication 1993). The geological asso­ciation of the Huitzila-La Lobera obsidian deposits may be de­bated. Recent work by geologists at the University of California, Berkeley, has revealed a broad range of geologic dates from vol­canic deposits in the vicinity including those consistent with ear­lier volcanism related to the formation of the Sierra Madre as well as dates indicative of more recent neovolcanic activity (Ian Carmichael, personal communication 1992).

Studies of obsidian deposits in the Sierra Madre Occidental are limited. Spence (1971, 1978) provides a brief description of the obsidian source area of Llano Grande located west of the modem city of Durango. Pastrana (1990) also acknowledges the presence of obsidian deposits within the Sierra Madre Occiden­tal. These he described as "yacimientos de n6dulos erosionados" to distinguish them from the younger neovolcanic sources to the south, which are less weathered or broken by postformation geomorphological processes. Despite Pastrana's prediction that a number of older mid-Tertiary obsidian flows should exist in northern Mesoamerica, prior to this study, no systematic inves­tigations of these sources had been completed.

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Physiographic Provinces

D Sierra Madre Occidental

B Trans-Mexican Neovolcanic Belt

Figure I. Obsidian sources of the southern Sierra Madre Occidental.

RECENT RESEARCH IN THE SOUTHERN SIERRA MADRE OCCIDENTAL

In 1992, field surveys and geological sampling conducted under the auspices of the Museum of Anthropology and the Phoenix Memorial Reactor Laboratory, University of Michigan, revealed a geographic region comprised of numerous broad surface ex­posures of weathered obsidian gravels (Darling 1992, 1993; Fig­ure 2). An intensive sampling program to collect samples for neutron activation analysis (NAA) was conducted across the source. A total of 50 collections was made from various sepa­rate source locations, or outcrops of material, in a rough north­south transect following the old road from Guadalajara, which passed through the former hacienda of La Lobera and the town of Huitzila. Using the road as a baseline, obsidian-gravel out­crops were identified as well as some buried deposits in eroded roadcuts. In general each collection spot was numbered and located using UTM grid coordinates. Supplemental samples at individual outcrops were collected in order to adequately rep­resent the broad range of colors and other physical character­istics that typify the Huitzila-La Lobera obsidians. Because of the highly eroded nature of the source, it was difficult to delin­eate individual outcrops or flow zones. For this reason, chem­ical analysis will be used to determine if geographically distinct chemical groups can be identified.

Two additional source locations within the Llano Grande source in southern Durango were also sampled for comparison from outcrops on the Cerro Navajas situated to the east of the broad Llano Grande basin (Figure 3). Generally, at both Huitzila-La Lobera and Llano Grande, each sample consisted of a total of 10 unmodified cobbles collected from the surface. Each sample represented a particular color or obsidian type present at each source location.

A program of chemical characterization analysis of the col­lected samples is currently underway. This study includes high­precision trace-element characterization of source samples and artifacts using NAA by the Phoenix Memorial Laboratory (PML), University of Michigan, and the Missouri University Re-

Darling

search Reactor (MURR), Columbia, Missouri . Samples of iden­tical material are being analyzed at both reactor facilities for comparisons to (I) enhance resolution of elements and chemi­cal patterns, (2) facilitate normalization of results, and (3) pro­vide the opportunity to test the interlaboratory calibration of obsidian analysis between the two laboratories. This will address recognized deficiencies in interlaboratory standardization and the need for greater comparability of analytical results from dif­ferent reactor and laboratory environments (Asaro et al. 1978; Cobean et al. 1991:82; Vogt et al. 1990).

Preliminary results of NAA have isolated at least two and possibly three chemically distinct groups in the Huitzila-La Lobera source, two of which are clearly separated geographi­cally (Michael Glascock, personal communication 1992). These include the Huitzila obsidian deposits in Zacatecas and the La Lobera sources located on the opposite side of the border in J alisco. The Llano Grande source also separates strongly from Huitzila-La Lobera. Additional analyses are underway to deter­mine possible chemical subgroups within each source as well as to examine the relationship of color and other attributes to chemical composition_

THE OBSIDIAN OF HUITZILA-LA LOBERA

The Huitzila-La Lobera region may be defined as a source area containing multiple obsidian outcrops with varying degrees of prehistoric utilization and differing trace-element chemistry (Sidrys et al. 1976). The source area covers approximately 480 square kilometers. However, additional, more intensive survey is necessary to better define the extent of obsidian deposits and their relation to each other and the geology of the region.

During fieldwork, collections were made in roughly three broad areas within the Huitzila-La Lobera region representing three distinct geographical groups: a northern group, a middle group, and a southern group. These groups represent high con­centrations of surface obsidian gravel and outcrops located on eroded slopes separated by drainages and alluviated valleys containing soil profiles, which can be several meters in thick­ness. Surface obsidian often appears in dense concentrations of rounded nodules that may exceed 20 cm in diameter, though most specimens are smaller fist-size cobbles or gravels (Fig­ure 4). A thick, white surface patination is not uncommon, but tends to vary with the soil environment and exposure to the el­ements. The patina is generally thickest on the upper surface of nodules or artifacts exposed to weather. Recently exposed cul­tural deposits as well as buried raw materials typically were less patinated than surface deposits.

The relationship of individual exposures or outcrops and buried deposits suggests that layers or lenses of obsidian may be regionally extensive. In the northern group of outcrops, south and west of the modern town of Huitzila, eroded obsid­ian could be found in the form of surface gravels. Nearby, in a heavily alluviated area known as the Mesa Tezezalco, similar, buried deposits of unutilized obsidian were observed in a strati­graphic layer 2.3-3.2 m below the surface in the profile of an eroded canal.

The second or middle group is a broad series of related, nearly contiguous outcrops distributed as a dense surface pave­ment around the Mesa Sin Nombre, the Mesa Pedernal, and the Cerro Espinazo de! Diablo. In this group, different colors of ob-

Obsidian sources of the southern Sierra Madre

'. i •,

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MWl Area above 2,000 meters

.l Outcrop/Obsidian sample number

• Modern Pueblo

• Modern Ranch

- - - - Unpaved Road

0 2KM

Figure 2. Map of the Huitzila-L.a Lobera obsidian source area showing geologic obsidian sample locations.

sidian nodules are highly mixed within relatively close proxim­ity of each other. For this reason, several source locations were collected and carefully mapped in order to obtain samples of ob­sidian that reflect variation in color and potentially in trace­element chemistry.

Lastly, the third group to the south and east of the ejido of La Lobera comprises a broad series of highly eroded exposures extending from the Cerro el Derrumbadero to Carbonera. Here four general areas were sampled. However, additional field re­connaissance and chemical study are necessary to clearly delimit

248

D Area above 1 .480 meters

'· ! i , .. \

. j

i ! i

A Outcrop/Obsidian sample number

• Modern Pueblo

• Modern Ranch

0 2 KM

Contour Interval • 80 meters

·· ...... _ .. , i

/ ( \

-··-'

·,

! ..I

! ··, (

· ·.i. i \ /

·· , . . I , . ..... ....... ...... , \ ..

Darling

Figure 3. Map of the Llano Grande obsidian source area showing geologic obsidian sample locations in the outcrops of Cerro Navajas.

Figure 4. Surface obsidian-gravel pave­ment in outcrops near Mesa Chinacatia­hua of the Huitzila-La Lobera obsidian source area. Note abundant fractured cobbles, large decortication flakes, an­gular debris, and unmodified now· banded nodules.

Obsidian sources of the southern Sierra Madre

the size of individual flows and the extent of prehistoric utili­zation.

Obsidian Raw-Material Characteristics and Color Variation

The Huitzila-La Lobera obsidian is unusual for its variability in color and quality. Variation is particularly pronounced with respect to differences in translucency, hue, and color of the ma­terial. For the most part, the obsidian is black and translucent to transparent. Nevertheless, there are a number of opaque types. These include brown to red or "mahogany" obsidian with black flow bands and gray to green opaque varieties with occa­sional beige to black banding or mottling. Other noticeable differences are the relative density of the material, cortical thick­ness , and flow banding in samples both between and within ob­sidian-gravel exposures. Flow banding in general was noted at all outcrops, although for individual nodules it is more or less pronounced or entirely absent.

Black varieties are also equally variable with respect to trans­lucency and range from very clear to cloudy depending on the density of microlites or other minute crystalline impurities. When backlit, the black obsidian often varies with respect to "hue," displaying a range of colors or tinting that primarily in­cludes a brownish-red tint, although green was also noted. Fi­nally, reflective properties of certain obsidian outcrops produce an effect resembling iridescence or opalescence. For the Mesa Sin Nombre outcrop this is expressed as a white or yellowish sheen that has an almost metallic look. A metallic sheen is also known for obsidians from sources in Hidalgo. At outcrops near Las Parejas and La Lobera a similar phenomenon produces in­tense colors or color banding. This effect is quite variable in color and intensity. Similar coloration may resemble the "rain­bow obsidian" of Llano Grande, Jalisco (not to be confused with Llano Grande, Durango), which also yields a deep blue ob­sidian and an opaque green variety (Weigand 1982a; P. C. Weigand, personal communication 1993).

The "Rainbow" Obsidian of La Mina, La Lobera

Iridescent colors are especially marked in the obsidian from La Mina, La Lobera. The sample must be turned in the light to see the intense colors that seem to emanate from within the ma­terial rather than reflect from its surface. Intense coloration appears to be caused in part by pronounced flow banding re­sembling layers or sheets in combination with high densities of microlites in the glass. However, both the banding and impu­rities do not seem to effect the quality of fracture.

Iridescent color was the most pronounced at outcrops in the south group near La Lobera but was also noted for some nod­ules in the north group associated with the Las Parejas outcrop and the Mesa Tezezalco. When turned so that a light source re­flects off the planar surface of the layers, nodules display in­tensely colored bands including blue, yellow, purple, and most commonly, green. In contrast, when turned so that the light shines across the plane of the layers, the obsidian appears black. Although flow banded, Las Parejas more typically displays sin­gle colors per nodule. Single-color nodules were also noted at La Mina as well as nodules with mottled color in which the var­ious bands appeared to be swirled or intermingled.

249

The iridescent obsidian at La Mina occurs within a broad surface outcrop of black obsidian gravel. Surface remains are dominated by prehistoric cultural debris as well as tailings and sorting piles of debris from recently renewed mining activities. Deeply buried deposits visible in recent mining pits reveal dense deposits of material including several large obsidian boulders measuring up to 2 min diameter. Larger blocks tend to be Jess strongly colored, with numerous phenocrysts that may have re­duced their utility for tool production.

Prehistoric exploitation of La Mina seemed to be in part di­rected toward obtaining the unusually colored raw material. This is suggested by extensive, deep deposits of flake debris within the relatively confined area of iridescent obsidian, mea­suring approximately 300 x 200 m. There is little evidence of prehistoric mining operations, although much of the prehistoric deposit has been disturbed by recent digging. Nevertheless, dense deposits of prehistoric flake debris containing numerous bifacial preforms are visible in recent mine pits to a depth of 30cm.

The "rainbow" obsidian of La Lobcra also presents an in­teresting technological problem for knapping. In order to pre­serve the iridescent color, the material must be worked so that the broad or flat sides of the tool are parallel with the plane of the flow bands. Otherwise the product will appear black in color rather than exhibiting the more stunning rainbow effect. A number of bifaces observed on the surface exhibit this colora­tion, suggesting that this may have been in part intentional.

OBSIDIAN OF THE LLANO GRANDE, DURANGO, SOURCE AREA

The obsidian of Llano Grande is clearly part of the upper mid­Tertiary volcanic deposits of the Sierra Madre Occidental and has been described in some detail by Spence (1971, 1978). Like the Huitzila-La Lobera obsidians, obsidian from the Llano Grande area appears primarily in broad expanses of surface gravels on low, eroded slopes with small nodules ranging up to 14 cm in diameter. Within the small area sampled on the Cerro Navajas, obsidian outcrops appear to be less variable in color and appearance overall than at Huitzila-La Lobera. Navajas ob­sidian is black and very clear, with few crystalline impurities. Occasional flow bands are present but arc not as common as in the Huitzila-La Lobera source.

PREHISTORIC UTILIZATION OF SIERRA MADRE SOURCES

Within the Huitzila-La Lobera source area the intensity of pre­historic utilization varies with the quality of the raw material present at each outcrop. Some outcrops display intensive obsid­ian working while others unsuitable for use in tool production display no prehistoric utilization. Factors that affected the se­lection of outcrops may include size of the nodules, color. and quality of fracture. Prehistoric procurement of obsidian ap­peared to be limited to exploitation of surface exposures. No ev­idence of prehistoric subsurface mining was found during this survey, although the large concentration of surface debris a.t the obsidian workshop at La Mina suggests that more intensive pro­cedures for extracting large obsidian nodules may have taken place there. As previously suggested, intensive working at La

250

Mina may have been in part influenced by the unusual color and high quality of the obsidian present.

Nearly all exposures of obsidian in both source areas dis­played evidence of utilization in the form of decortication flakes, cores, occasional irregular blade cores, tested nodules, and some reworked flakes. Numerous bifaces and biface blanks as well as some unifacially retouched blade blanks were also present at a number of outcrops in both of these source areas (Figure 5). Whole or nearly finished artifacts including small projectile points with thinning or pressure flaking were rare, suggesting that few artifacts were ever completed at the source. In part due to the limitations of the size of nodules available and perhaps the fracture pattern, as suggested for Llano Grande (Spence 1971), no evidence for macrocore preparation for the production of prismatic blades was encountered. However, in this portion of the northern frontier , prismatic-blade technol­ogy is not characteristic of the few lithic assemblages that have been analyzed (Spence 1971). Prismatic blades have been found in small quantities at several sites in the Tlaltenango and Juchipila valleys northeast of Huitzila as well as at the sites of La Quemada and Alta Vista even further to the north. In gen­eral, these are considered imports into the region, and additional studies are required to test whether or not a prismatic-blade in­dustry existed in the northern frontier.

Figure 5. Obsidian bifaces from the prehistoric workshop located at La Mina, La Lobera. Note variable patination of selected artifacts.

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Undoubtedly biface blanks or preforms produced at these sources were subsequently removed and finished elsewhere. Typically, these bifaces are large, lenticular, retouched flakes often with a high ridge down the center of the dorsal side and a prominent bulb of percussion on the ventral side. Many ap­pear to have been broken during production or discarded due to flaws in the material or workmanship.

Biface blanks are common a t quarry sites throughout the New World and are generally accepted as "rough-outs," which were later finished into a variety of artifact types (Holmes 1894, 1900, 1919; Singer and Ericson 1977 ; Torrence 1986). For ex­ample, this pattern is present at the El Chaya) obsidian source in Guatemala where the production of macrocores or preforms at quarries was followed by the final production stages at other locations (Coe and Flannery 1964; Sheets 1975:100-102). Sim­ilarly, the bi face blanks of H uitzila-La Lober a and Llano Grande resemble the preforms described at the Hacienda Metepec workshops located on the outskirts of Teotihuacan (Rattray 1989). These exhibit similar retouch on the dorsal side with a marked bulb of percussion visible on the ventral surface. Transport of at least a portion of these biface blanks from the Otumba quarries for the final stages of completion has been suggested by Rattray (1989:245). The manufacture of rough­outs is a practical method of preprocessing that facilitates se­lection of raw material, reduces weight for transport, and possibly enhances exchange value (Torrence 1986: 186-187).

As noted by Holmes (1919) and Torrence (1986), the relative presence of failed macrocores, preforms, or other classes of ar­tifacts at quarry sites will be an expression of the relationship among the raw material, the technological system, and the de­sired products. For this reason both the limitations of these highly weathered sources in the Sierra Madre Occidental, which were exploited prehistorically, and the lithic technology of the northern frontier are reflected in the kinds of artifacts or pre­forms that were produced at Llano Grande and Huitzila-La Lobera (Pastrana 1990).

Holmes (1894, 1919) and others suggest that it is difficult to predict the final products from biface blanks given their gen­eralized nature and ubiquity at many quarry sites. Thus, biface blanks may be of limited utility as diagnostics indicative of par­ticular cultural complexes or phases. Yet , similar to the Haci­enda Metepec, evidence for finishing of preforms or even biface workshops may be expected at sites in the northern frontier. Previous identification of unfinished bi face blanks at archae­ological sites in the north as diagnostics, projectile points, or knives for which they may have been used secondarily could be misleading, and could lead to the misidentification of other ac­tivities including the final stages of tool production.

TRADE AND EXCHANGE OF OBSIDIAN IN THE NORTHERN PERIPHERY

Issues concerning the distribution of obsidian in the northern periphery of Mesoamerica have been considered by Trombold et al. (1993) and Spence (1971, 1978), respectively. Both agree that movement of obsidian from the Zacatecas and Durango sources is limited and is restricted primarily to networks centered in the northern region . This contrasts with the exchange of glass from more distantly located sources in the Trans-Mexican Neo­volcanic Belt to the south including La Joya in Jalisco (Weigand and Spence 1982).

Spence (I 971, 1978) observes that utilization of Llano

Obsidian sources of the southern Sierra Madre

Grande obsidian is limited to local groups in Durango, although there is some suggestion of trade with other areas to the north as far as Casas Grandes. Neutron activation analysis supports this observation confirming that Llano Grande supplied the ma­jority of obsidian appearing at the Chalchihuites sites of the Guadiana Valley and at nearby sites of the Las Animas, Adams, and Loma San Gabriel culture complexes (Spence 1978: 185; cf. Pires-Ferreira 1975). Obsidian-hydration dates based on a rate developed at the Schroeder site for Llano Grande obsidian ap­pearing at various sites in the region span much of the Classic and Postclassic (A.O . 200-1100; Spence 1978).

As one moves away from the source, use by prehistoric groups of Llano Grande obsidian drops significantly. Thus in the Chalchihuites region in northwestern Zacatecas, the pres­ence of obsidian at Alta Vista phase sites (A.O. 750-850; Kelley 1985:27 5) decreases and is generally limited to sites of presum­ably greater ceremonial and political importance. In somewhat later archaeological assemblages, obsidian from the south in the form of finished fine blades (possibly from sources in Jalisco and Nayarit) appears to increase (Spence 1971 :23-24). This is in part a result of the Postclassic expansion of extraregional trade from sources such as La Joya in the south (Spence et al. 1982). Movement of obsidian from less-distant sources includ­ing Huitzila-La Lobera either as finished tools or raw material into the Chalchihuites area remains to be explored.

Further to the south, Huitzila-La Lobera obsidian is also dis­tributed locally within the valleys of southern Zacatecas and northern Jalisco. Based on trace-clement chemistry, artifacts from sites in the Bolanos Valley to the northwest, and the Juchipila and Malpaso valleys to the northeast clearly match two of the chemical groups identified in the Huitzila-La Lobera source area (Michael Glascock, personal communication 1992; Trombold et al. 1993). Dated occupations at these sites based on ceramic correlations and radiocarbon dates suggest a time span of roughly the first centuries A.O. to A.O. 900 (Kelley 1971; Trombold 1990).

SIGNIFICANCE TO REGIONAL ARCHAEOLOGY

The recognition of two obsidian source areas in the northern frontier adds an intriguing facet to the problem of understand­ing the evolution of the cultures of the Mesoamerican periph­ery. Obsidian is not a rare resource in the northern frontier of Mesoamerica, yet it was never exploited to the degree observed in central and western Mesoamerican sources. Specifically, pris­matic-blade production or the production of macrocores to pro­duce prismatic blades is not characteristic of either of the source areas examined. This is in part attributable to the highly eroded condition of sources available in the Sierra Madre Occidental and the method of raw-material extraction. Yet , elaborate min­ing techniques like those in the mines of the Chalchihuites area to extract hematite, malachite, chert, pyrite, and other miner­als could have been used to reach potentially higher-quality, buried obsidian deposits (Gamio 1910; Weigand 1982a).

Weigand (personal communication 1993), Spence (1971), and Pastrana (1990) generally agree that for known sources in the southern Sierra Madre Occidental the low quality of obsidian, particularly of its fracture qualities, prohibits the production of prismatic blades. This may be true for some sources. However, one must take into account not just the quality of material avail­able or the requirements for raw-material extraction but the technological system involved in the production of obsidian

251

items. The absence o f prismatic blades at northern Mesoamer­ican sites made from local material may suggest the lack of ap­propriate technological skill, knowledge, need and/or suitable "high-quality" obsidian, or both. As Weigand suggests, among the numerous known low-quality obsidian sources in Mesoamer­ica, a high-quality source may constitute a "rare resource" (Weigand 1982b:2). This may be true for areas that rely on spe­cific qualities or kinds of obsidian or in areas where prismatic blades are a common component of the artifact assemblage.

As more obsidian sources are recognized a more explicit method for evaluating "quality," which accounts for the phys­ical properties of the material including fracture mechanics, en­vironment and aging, and its utility for particular stone-tool technologies, is needed. Additional source-location data on pris­matic blades at northern Mesoamerican sites, preferably using techniques such as NAA, is also necessary to examine hypoth­eses concerning production, distribution, and exchange of both local and exotic varieties of obsidian.

Modest levels of local exchange of raw material in the form of nodules and perhaps biface blanks to large administrative centers including Alta Vista and Las Ventanas is balanced by similarly low levels of exchange of exotic obsidian into the north from the Tequila sources (Spence 1971; Trombold et al. 1993). The presence of Tequila obsidian in Durango during the Epi­classic and Postclassic is in part explained by exchange networks identified by Kelley (1986:85), which bypassed the southern val­leys of Zacatecas following routes along the Pacific Coast into the highlands. The appearance of other rare obsidian artifacts including those which visually resemble obsidian from Pachuca, Hidalgo, sources has also been tentatively identified (Jimenez Betts, personal communication 1993, based on visual identifi­cation by Joaquin Garcia-Barcena).

In contrast , locally based trade of obsidian to the north along the eastern flank o f the Sierra from more closely situated sources such as Huitzila-La Lobera during the Classic period re­mains to be investigated. Clearly the apparent distribution of Huitzila-La Lobera obsidian to sites throughout the southern valleys of Zacatecas and Jalisco indicates that it was available to the cultural systems of the northern frontier. Yet, little can be said at this time about the organization of distributional net­works and production.

Distribution of Huitzila-La Lobera obsidian suggests a pre­viously unrecognized unity among the cultures of the north that crosscuts previously defined cultural barriers. Specifically, the Teuchitlan culture situated in the highland lake district in north­ern Jalisco and in the Bolanos and Valparaiso canyons to the north (Cabrero Garcia 1989; Weigand 1985) is distinct from the eastern valleys of the "Caxcan Archaeological Zone" defined by Kelly (1948). This east-west divide encompasses the northern portion of a frontier separating the areas of western and cen­tral Mesoamerican influence based largely on the distribution of shaft tombs, figurine styles, and architectural patterns (Schondube 1980; Weiga11d 1985). The development of a hard frontier in this area during the Classic period is depicted in part as a response by the Teuchitlan system to the expanding metrop­olis of central Mesoamerica and pressure from Teotihuacan­influenccd groups in the west (Weigand 1985:90). Nevertheless increasing evidence for interaction across this frontier - includ­ing the distribution of obsidian - suggests that this separation during the Classic period at least in the drainages north of the Rio Santiago was not as pronounced as previously supposed.

The distribution of Huitzila-La Lobera obsidian is also of

252

importance in defining the relationship of far northern Meso­america to central, more complex systems including Teotihua­can during the Classic period. Based on a few studies of lithics in the northern frontier, obsidian never obtained the same sig­nificance in the north that it had in the core areas to the south. Yet, this contrasts with the view that much of the sociopoliti­cal development of the cultures of Zacatecas and southern Durango was due to the expansion or diffusion of the Meso­american cultural sphere through colonization, trading enclaves, or in the form of a developing world system (Cabrero Garcia 1989; Jimenez Betts 1989; Kelley 1974; Nelson 1993). These ap-

RESUMEN

Este articulo considcra los yacimientos de obsidiana de la Sierra Madre Occidental sur y sus relaciones con las culturas pre-hispanicas de la fron­tera septentrional de Mesoamerica. Especificamente, las rcgiones geolog­icas que contienen yacimicntos de obsidiana incluyen Huitzila-La Lobera, estados de Zacatecas y Jalisco, y Llano Grande, en Durango. La obsidiana de Huitzila-La Lobera se caracteriza por su variedad de colores. En particular, la "rainbow obsidian" u obsidiana iridiscente de

ACKNOWLEDGMENTS

Fieldwork was conducted in two seasons in 1991 and 1992. Support for fieldwork in 1991 was provided by the University of Michigan, Marga­ret Wray French Scholarship Fund, the Program for Latin American and Caribbean Studies, and the Rackham School for Graduate Stud­ies. A Sigma Xi Grant-in-Aid of Research also provided funds to sup­port the first field season. Geologic survey, sampling, and NAA in 1992 were sponsored by the Phoenix Memorial Laboratory (PML) Grants for Peaceful Applications of Nuclear Energy, University of Michigan. Funds to support interlaboratory comparisons between PML and the Missouri University Research Reactor Facility (MURR) were supplied by the Na­tional Science Foundation. I would like to thank Dr. Jeffrey R. Parsons and Dr. Joyce Marcus, Museum of Anthropology, University of Mich­igan; Dr. Ronald Fleming, director of the PML; and Dr. Michael D. Glascock, group leader of the MURR Archaeomctry Laboratory, for their generous support of all phases of this project. This study greatly benefited from conversations with members of the Geology Department, University of Michigan, including discussions with Dr. Rebecca Lange. I would also like to thank Dr. Ian Carmichael of the University of Cal­ifornia, Berkeley, as well as Dr. M. James Blackman of the Smithson-

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La Mina, La Lobera, Jalisco es distintiva. Ambas areas muestran aprovechamiento pre-hispanico incluyendo la manufactura de artefactos de obsidiana tal como prcformas bifaciales, lascas y cl desgaste de n6dulos de materia prima. lmplicaciones para el entendimiento de utilizacion pre-hispanica y la distribuci6n de obsidiana de yacimicntos de la Sierra Madre Occidental en la frontcra septcntrional de Meso­america son presentadas y cxaminadas.

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