Não informado. (1999). United States Geological Survey annual report. U.S. Geological Survey.
शिकागो शैली (17वां संस्करण) प्रशस्ति पत्रNão informado. United States Geological Survey Annual Report. Washington: U.S. Geological Survey, 1999.
एमएलए (8वां संस्करण) प्रशस्ति पत्रNão informado. United States Geological Survey Annual Report. U.S. Geological Survey, 1999.
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