Yellowstone National Park in northwest Wyoming currently lies above a source of magma called a hot spot or a plume. The giant volcanic depression that contains the park and its geysers and hot springs (for example, Old Faithful) formed about 100,000 to 5 million years ago. Over the last 16 million years, the North American Plate has moved westward over this plume, creating the Snake River Plain. The Yellowstone caldera (indicated by the red outline) is a large crater-like feature covering more than 1300 square miles. It formed when an underground magma chamber collapsed 630,000 years ago.