Geology is the study of the Earth, its various landforms, rocks, and what has happened to them over time.
Geologic processes shape the landscape through volcanic activity, rock formation, mountain building, erosion and interaction with living organisms.

Throughout the Greater Yellowstone Network, many different geologic processes are occurring at the same time, in different proportions. The juxtaposition of ancient bedrock and young mountains gave rise to the jagged Teton Range. The collision of continental plates formed metamorphic gneiss and igneous granite—some of the oldest rocks in North America. In Bighorn Canyon National Recreation Area a basement complex of igneous and metamorphic rocks were also uplifted to form the Bighorn Mountains; the subsequent erosion carves the Bighorn Canyon. Yellowstone National Park’s physical landscape is home to some of the Earth’s most active volcanic, hydrothermal (water + heat), and earthquake systems. While these mountains and canyons may appear to change very little during our lifetime, they are still highly dynamic and variable.