Swineford, Ada, and John C. Frye. “Petrographic Comparison of Pliocene and Pleistocene Volcanic Ash from Western Kansas”. Bulletin (Kansas Geological Survey), no. 64 (January 1, 1946): 1–32. Accessed January 2, 2026. https://journals.ku.edu/kgsbulletin/article/view/21978.