This map is a product of a cooperative project of the U.S. Geological Survey, the U.S. National Park Service, and the Bureau of Land Management to provide geologic map coverage and regional geologic information for visitor services and resource management of Grand Canyon National Park, Lake Mead National Recreation Area, Grand Canyon-Parashant-National Monument, and adjacent lands in northwestern Arizona. This map is a synthesis of previous and new geologic mapping that encompasses the Peach Springs 30' x 60' quadrangle, Arizona. The geologic data will support future geologic, biologic, hydrologic, and other science resource studies of this area conducted by the National Park Service, the Hualapai Indian Tribe, the Bureau of Land Management, the State of Arizona, and private organizations. The Colorado River and its tributaries have dissected the southwestern Colorado Plateau into what is now the southwestern part of Grand Canyon. The erosion of Grand Canyon has exposed about 426 m (1,400 ft) of Proterozoic crystalline metamorphic rocks and granite, about 1,450 m (4,760 ft) of Paleozoic strata, and about 300 m (1,000 ft) of Tertiary sedimentary rocks. Outcrops of Proterozoic crystalline rocks are exposed at the bottom of Grand Canyon at Granite Park from Colorado River Mile 207 to 209, at Mile 212, and in the Lower Granite Gorge from Colorado River Mile 216 to 262, and along the Grand Wash Cliffs in the southwest corner of the map area.