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2003. United States. Environmental Protection Agency. This polygon shapefile shows Omernik's Level III ecoregions, derived from a 1:7,500,000 map created by J.M. Omernik in 1987 and from refinements of... National Atlas of the United States.
1568. Geological Survey (U.S.). This point shapefile contains the locations and attributes of significant, historic earthquakes that caused deaths, property damage, and geological... National Atlas of the United States.
1990. United States. Agricultural Research Service. This polygon shapefile portrays the spread, by year, of the Africanized honey bee (AHB) in the United States, Puerto Rico, and the U.S. Virgin Isla... National Atlas of the United States.