31. 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.).