Williams, I. A., & Allen, J. E. (1991). Geologic history of the Columbia River Gorge, as interpreted from the historic Columbia River scenic highway (3rd ed., rev.). Oregon Historical Society Press.
शिकागो शैली (17वां संस्करण) प्रशस्ति पत्रWilliams, Ira A., और John Eliot Allen. Geologic History of the Columbia River Gorge, as Interpreted from the Historic Columbia River Scenic Highway. 3rd ed., rev. Portland, Or.: Oregon Historical Society Press, 1991.
एमएलए (8वां संस्करण) प्रशस्ति पत्रWilliams, Ira A., और John Eliot Allen. Geologic History of the Columbia River Gorge, as Interpreted from the Historic Columbia River Scenic Highway. 3rd ed., rev. Oregon Historical Society Press, 1991.
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