This symposium was held April 18-20, 2019 at the Shrine of the Ages Auditorium at the South Rim of Grand Canyon in honor of Grand Canyon National Park’s 2019 Centennial celebration, the 150th anniversary of John Wesley Powell’s 1869 pioneering Colorado River expedition, and Earth Day 2019. The conveners were Karl Karlstrom and Laurie Crossey, University of New Mexico, Steven Semken, Arizona State University, Todd Stoeberl, Chief of Interpretation, and Jeanne Calhoun, Chief of Science...