Death Valley National Park is an American national park that straddles the California–Nevada border, east of the Sierra Nevada. The park boundaries include Death Valley, the northern section of Panamint Valley, the southern section of Eureka Valley and most of Saline Valley. The park occupies an interface zone between the arid Great Basin and Mojave deserts, protecting the northwest corner of the Mojave Desert and its diverse environment of salt-flats, sand dunes, badlands, valleys, canyons and mountains. Death Valley is the largest national park in the contiguous United States, as well as the hottest, driest and lowest of all the national parks in the United States. It contains Badwater Basin, the second-lowest point in the Western Hemisphere and lowest in North America at below sea level. More than 93% of the park is a designated wilderness area. The park is home to many species of plants and animals that have adapted to this harsh desert environment including creosote bush, Joshua tree, bighorn sheep, coyote, and the endangered Death Valley pupfish, a survivor from much wetter times. UNESCO included Death Valley as the principal feature of its Mojave and Colorado Deserts Biosphere Reserve in 1984. A series of Native American groups inhabited the area from as early as 7000 BC, most recently the Timbisha around 1000 AD who migrated between winter camps in the valleys and summer grounds in the mountains. A group of European Americans, trapped in the valley in 1849 while looking for a shortcut to the gold fields of California, gave the valley its name, even though only one of their group died there. Several short-lived boom towns sprang up during the late 19th and early 20th centuries to mine gold and silver. The only long-term profitable ore to be mined was borax, which was transported out of the valley with twenty-mule teams. The valley later became the subject of books, radio programs, television series, and movies. Tourism expanded in the 1920s when resorts were built around Stovepipe Wells and Furnace Creek. Death Valley National Monument was declared in 1933 and the park was substantially expanded and became a national park in 1994. The natural environment of the area has been shaped largely by its geology. The valley is actually a graben with the oldest rocks being extensively metamorphosed and at least 1.7 billion years old. Ancient, warm, shallow seas deposited marine sediments until rifting opened the Pacific