Reynolds, Rick; Janice Elvidge, Krista Reynolds eds. (2021). Investigating Ice Age Floods (PDF) 11. National Park Service, U.S. Department of the Interior. Retrieved on 2023-09-16. "Hands-On Science Lessons Adaptable for Grades K -12". p. 13 of document, p. 11 of PDF. Doesn't explicitly mention license (says, rather generically, "Wikimedia Commons"), but links file page.
