Cedar Breaks National Monument is a U.S. National Monument located in the U.S. state of Utah near Cedar City. Cedar Breaks is a natural amphitheater, stretching across 3 miles (4.8 km), with a depth of over 2,000 feet (610 m). The elevation of the rim of the amphitheater is over 10,000 feet (3,000 m) above sea level. The eroded rock of the amphitheater is more eroded than, but otherwise similar to formations at nearby Bryce Canyon National Park, Red Canyon in Dixie National Forest and select areas of Cedar Mountain (SR-14). Because of its elevation, snow often makes parts of the park inaccessible to vehicles from October through May. Its rim visitor center is open from June through October. Several hundred thousand people visit the monument annually. The monument area is the headwaters of Mammoth Creek, a tributary of the Sevier River. 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 was deposited at the bottom of an ancient 70 by 250 miles (110 km × 400 km) lake, known as Lake Claron about 60 million years ago. It continues to erode at a pace of about 2 inches (50 mm) every 5 years. Atop the plateau, volcanic rock known as rhyolitic tuff covers much of the area, formed during cataclysmic eruptions around 28 million years ago. The area is a form of badlands—canyons, spires, walls, and cliffs so steep and confusing that the lands, while of great aesthetic value, are of little utilitarian worth. Early settlers called them badlands or breaks and created its current name by combining breaks with cedar for the many juniper trees (often incorrectly called cedars) that grow in the area.