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2003. Geological Survey (U.S.) Minerals Information Team. This point shapefile represents the locations of refractory, abrasive, and other industrial minerals operations in the United States. The data repr... National Atlas of the United States.
2002. Geological Survey (U.S.) Minerals Information Team. This point shapefile includes sand and gravel operations in the United States. These data were obtained from information reported voluntarily to th... National Atlas of the United States.