The Trail of Time exhibition under construction at Grand Canyon National Park is the world's largest geoscience exhibition at one of the world's grandest geologic landscapes. It is a 2-km-long interpretive walking timeline trail that leverages Grand Canyon vistas and rocks to guide visitors to ponder, explore, and understand the magnitude of geologic time and the stories encoded by Grand Canyon rock layers and landscapes. As one of a new generation of geoscience education exhibits, the Trail of Time targets multiple cognitive and affective levels with accurate content, active geoscience inquiry and interpretation, and place-based cultural integration. It developed as an outgrowth of sustained geoscience research funded by the National Science Foundation, with scientists as the conceivers and coordinators of the project. It benefits from a high level of synergy with the National Park Service interpretation division, as well as extensive on-site and off-site evaluation of pedagogic effectiveness in the outdoor informal science environment. The Trail of Time will impact many of the five million annual visitors to the National Park. Associated cognitive research on public understanding of “deep time” offers opportunities to inform more effective geoscience pedagogy for informal and formal educational settings.