The isotopic constitutions of Pb in galenas from W.-central New Mexico appear to be related to the location of the samples. "Modern" leads forms a belt bounded on either side by "anomalous" leads. The "modern" Pb belt extends for more than 130 mi. and lies essentially along a line defined by the towns of Alamogordo and Socorro, New Mexico. Geologists have postulated a regional lineament to lie under the belt defined by the "modern" Pb samples. This structure is known variously as the Zuni, Zuni-Sacramento, or New Mexico-Utah lineament in the literature. It is proposed that Pb isotopes can show a rational geological control and thus should be among the interpretative tools of tectonophysicists and geologists.