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New Thellier-Coe archeointensity determinations have been measured on 15 potsherds from the Oaxaca Valley belonging to three of the four Formative Periods (Pre-Classical) of Mesoamerica, spanning 1400–700 BC. Seven of these are considered to be reliable and indicate a geomagnetic field strength of about 30 μT. This value is some 75% of the present geomagnetic field strength but is in agreement with the absolute intensities predicted from global models for this time and location, and consistent with coeval published determinations. These data thus provide significant evidence for the geomagnetic field strength in an area and for a time that was previously poorly constrained, thus providing an important contribution towards establishing a local master curve for the last 3500 yr. When established, such a curve would be a useful dating tool and also enable establishing for field strength correlations with climatic events and civilization evolutions in a region that is particularly strong in archeological and geological features. Such potential is examined for aridity events, although such observations can only be considered tentative at this stage.

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