This project will produce new information about climatic changes and human impacts along the Northern Frontier of Mesoamerica, A.D. 500-900, a period when civilization touched areas previously populated by small farming villages and bands of hunter-gatherers. In Guanajuato, Jalisco, Zacatecas, and Durango, Mexico, large ceremonial centers sprang up, surrounded by clusters of population. One such population cluster around the site of La Quemada, Zacatecas, is the scene for this study. Between A.D. 500-900, a large community dominated the valley and its tributaries with a monumental ceremonial center, roadways, extensive terrace systems, and over 200 villages along the Malpaso River. Professor Ben Nelson and doctoral candidate Michelle Elliott of Arizona State University, along with Professor Christopher Fisher of Kent State University, will collaborate with geologist Roberto Molina of the National Autonomous University, to collect plant remains, sediments, magnetic samples, and charcoal for radiocarbon dating and to create a geological map of the area. They and other scientists will analyze the samples to test hypotheses about changes in vegetation, erosion, floodplain characteristics, and fires that occurred before, during, and after a period of intensive human settlement around La Quemada. They will recover this information by cutting trenches in the floodplain as well as by surveying the landscape to record landforms and parent materials that may have contributed to the accumulation of sediments and soils in the floodplain. Their goal is to reconstruct the history of that accumulation and its relationship to human occupation. Archaeologists have long suspected that the changes in the environment played a role in civilization's fluctuations in this region. They hypothesize that colonists settled the frontier during a period of increased rainfall and that several centuries later, a climatic reversal led to the region's abandonment. Since Pedro Armillas formulated this "arid margin" hypothesis, archaeologists have learned a great deal the settlements centered on La Quemada. Recent research has clarified many aspects of this occupation, but the information is inadequate to address the arid margin hypothesis. The collected materials will allow systematic evaluation of this hypothesis with several independent classes of data, including pollen, phytoliths, macrobotanical remains, magnetic susceptibility, sediment characterization, and radiocarbon assays. Archaeologists have not investigated ancient environmental change in any part of the Northern Frontier in such a comprehensive way. To the north of the study area, studies of desert streams in the American Southwest indicate precipitation flux for this period; to the south, lake deposits contain evidence for potentially related events. Experience shows, however, that events in one valley or lake cannot be readily predicted from those in another. This study will provide information that will ultimately allow evaluation of human-environmental interactions on a long time scale over a wide region. The investigators plan to communicate their findings not only to people in their own profession, but to a range of ecologists, geologists, geographers, government officials, and interested community members.
