Betts, R. B. (1985). In search of York: The slave who went to the Pacific with Lewis and Clark. Colorado Associated University Press.
शिकागो शैली (17वां संस्करण) प्रशस्ति पत्रBetts, Robert B. In Search of York: The Slave Who Went to the Pacific with Lewis and Clark. Boulder, Colo.: Colorado Associated University Press, 1985.
एमएलए (8वां संस्करण) प्रशस्ति पत्रBetts, Robert B. In Search of York: The Slave Who Went to the Pacific with Lewis and Clark. Colorado Associated University Press, 1985.
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