Reynolds, Rick; Janice Elvidge, Krista Reynolds eds. (2021). Investigating Ice Age Floods (PDF) 16. National Park Service, U.S. Department of the Interior. Retrieved on 2023-09-16. "Hands-On Science Lessons Adaptable for Grades K -12". p. 18 of document, 16 of PDF. Doesn't explicitly mention license (says, rather generically, "Wikimedia Commons"); clearly intends to link file page, but link is broken.
