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.
توثيق أسلوب شيكاغو (الطبعة السابعة عشر)Williams, Ira A., و 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.
توثيق جمعية اللغة المعاصرة MLA (الطبعة الثامنة)Williams, Ira A., و 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.
تحذير: قد لا تكون هذه الاستشهادات دائما دقيقة بنسبة 100%.