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Big Bend National Park in the U.S. state of Texas has national significance as the largest protected area of Chihuahuan Desert topography and ecology in the United States. It contains more than 1,200 species of plants, more than 450 species of birds, 56 species of reptiles, and 75 species of mammals.〔 〕 The national park covers .〔 A variety of Cretaceous and Cenozoic fossil organisms exist in abundance, and the park has artifacts estimated to be 9,000 years old. Historic buildings and landscapes offer graphic illustration of life along the international border in the 19th century. For more than , the Rio Grande/Río Bravo forms the international boundary between Mexico and the United States, and Big Bend National Park administers approximately along that boundary. The park was named after the area, which is bounded by a large bend in the river and Texas-Mexico border (''see map at right below''). Because the Rio Grande serves as an international boundary, the park faces unusual constraints while administering and enforcing park rules, regulations, and policies. In accordance with the Treaty of Guadalupe Hidalgo, the park's territory extends only to the center of the deepest river channel as the river flowed in 1848. The rest of the land south of that channel, and the river, lies within Mexican territory. ==Geography and climate== The park exhibits dramatic contrasts and its climate may be characterized as one of extremes. Dry and hot late spring and summer days often exceed in the lower elevations. Winters are normally mild but subfreezing temperatures occasionally occur. Because of the range in altitude from about along the river to Emory Peak in the Chisos Mountains at ,〔 a wide variation in available moisture and temperature exists throughout the park. These variations contribute to an exceptional diversity in plant and animal habitats. Some species in the park, such as the Chisos oak (''Quercus gravesii''), are found nowhere else in the United States. The of river that form the southern park boundary include the spectacular canyons of Santa Elena, Mariscal, and Boquillas. The Rio Grande, which meanders through this portion of the Chihuahuan Desert, has cut deep canyons with nearly vertical walls through three uplifts made primarily of limestone. Throughout the open desert areas, the highly productive Rio Grande riparian zone includes numerous plant and animal species and significant cultural resources. The vegetative belt extends into the desert along creeks and arroyos. South of the border lie the Mexican states of Chihuahua and Coahuila and newly protected areas for flora and fauna, which are regions known as the Maderas del Carmen and the Cañón de Santa Elena. In 2012, the park was named as an international dark-sky park by the International Dark-Sky Association, which recognized the park as one of only ten places in the world certified for dark-sky stargazing. In addition, the association recognized the park as having the darkest measured skies in the lower 48 United States. On many nights, park visitors can look up to the night's sky to see thousands of stars, bright planets, and the clear outline of the Milky Way band. Astronomers, both professional and amateur, are seen on many moonless nights gazing up at the stars through portable telescopes. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Big Bend National Park」の詳細全文を読む スポンサード リンク
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