The amphitheater, located near the west end of the Colorado Plateau, covers the west side of the Markagunt Plateau, the same plateau that forms parts of Zion National Park. Uplift and erosion formed the canyon over millions of years, raising and then wearing away the shale, limestone, and sandstone that were deposited at the bottom of an ancient lake, known as Lake Claron, about 60 million years ago. It continues to erode at a pace of about every 5 years. Atop the plateau, much of the area is covered by volcanic rock known as rhyolitic tuff, formed during cataclysmic eruptions around 28 million years ago.