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Start Over Year 1990 Resource Class Datasets Subject Plate tectonics
1974, 1975, 1976, 1977, 1978, 1979, 1980, 1981, 1982, 1983, 1984, 1985, 1986, 1987, 1988, 1989, 1990, 1991, 1992, 1993, and 1994. King, Philip B., Arndt, Raymond E., Schruben, Paul G., Bawiec, Walter J., and Beikman, Helen M. This polygon shapefile shows the boundaries of geologic units within the United States. This layer is part of the Geologic Map of the United States... Geological Survey (U.S.).