Reynolds, Rick; Janice Elvidge, Krista Reynolds eds. (2021). Investigating Ice Age Floods (PDF) 15. National Park Service, U.S. Department of the Interior. Retrieved on 2023-09-16. "Hands-On Science Lessons Adaptable for Grades K -12". p. 17 of document, 15 of PDF. Doesn't explicitly mention license (says, rather generically, "Wikimedia Commons"), but links file page.
