1. Outlines of Major Calderas and Impact Structures: Generalized Geologic Map of the Conterminous United States, 2005
2005. King, Philip B., Arndt, Raymond E., Schruben, Paul G., Bawiec, Walter J., and Beikman, Helen M. This line shapefile shows the outlines of major calderas and impact structures in the United States. A caldera is a large, generally circular depre... Geological Survey (U.S.).
2004. National Atlas of the United States. This point shapefile includes Holocene volcanoes, which are those thought to be active in the last 10,000 years, that are within an extended area o... National Atlas of the United States.