Reynolds, Rick; Janice Elvidge, Krista Reynolds eds. (2021). Investigating Ice Age Floods (PDF) 106. National Park Service, U.S. Department of the Interior. Retrieved on 2023-09-16. "Hands-On Science Lessons Adaptable for Grades K -12". p. 106 of document, 104 of PDF. Doesn't explicitly mention license (says, rather generically, "Wikimedia Commons") but links to file page.