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The Mezquital Valley (Otomi: B’ot’ähi) is a series of small valleys and flat areas located in Central Mexico, about north of Mexico City. It is part of the central Mexican highlands, with altitudes between and above sea level. It is one of Mexico's main semi-arid/area regions, whose native vegetation is dominated by cactus species, mesquite trees, and maguey with pine and oak trees in the highest elevations. It is considered to be part of the northern extension of Mesoamerica, with one major archeological site, Tula, which was the main city of the Toltecs, an important influence for the later Aztecs. However, from the Aztec period to the 20th century, it was sparsely populated and very poor, with one main indigenous ethnicity, the Otomis. In the 20th century, irrigation works were created to take advantage of the water in the Tula River, along with wastewater drained from the Valley of Mexico for agriculture. Today the valley produces various grains and produce, including one-quarter of all green chili peppers grown in Mexico. ==Geography and environment== The Mezquital Valley is located in the central Mexican Highlands about north of Mexico City.〔 〕 It covers in the west of the state of Hidalgo and small portions extending into the State of Mexico and Querétaro.〔 〕 With an altitude of between above sea level, it is part of the Trans-Mexican Volcanic Belt.〔 The valley consists of smaller valleys such as the Actopan, Ixmiquilpan, and the Tasquillo, along with some flatlands.〔 〕 What unifies the region is its waterways, such as the Tula and Alfajayucan rivers, as well as streams such as the Alfajayucan, Arroyo Zarco, Rosas and Salado, as well as history and culture.〔 It is one of the four main arid/semi arid regions of Mexico, along with Baja California, the Tehuacán-Cuicatlán Valley, and the Chihuahua Desert. These four regions together account for 60 percent of Mexico's territory.〔 〕 The average annual precipitation of the valley is , less than half of the state average of .〔 〕 In the elevations of surrounding mountains between , the climate is temperate and moister, with rains in the summer. Below this level, the area is semi-arid steppe.〔 The valley is drained by the Tula River.〔 The vegetation of the valley is divided into zones. Forests of pine and oak dominate the higher mountain areas. The lower valley floor is semi-arid except for areas along riverbanks which have some tropical vegetation. In some canyons, thermal inversion also allows for a more humid climate.〔 Dominant vegetation includes various cacti, mesquite, and maguey, as most of the valley is dry.〔 Other important wild species include cypresses (''Taxodium mucronatum'' and ''Cupressus'' spp.), pine (''Pinus'' spp.), willow (''Salix'' spp.), oak (''Quercus'' spp.), huisache (''Vachellia farnesiana''), cardón (''Ilex'' or ''Pachycereus'' spp.), barrel cactus (''Echinocactus'' spp.), yucca (''Yucca'' spp.), huapilla (''Hechtia'' spp.), cucharilla (''Dasylirion'' spp.), cat's claw (''Mimosa'' spp.), zacate (''Setaria'' spp. or ''Muhlenbergia macroura''), chipil (''Crotalaria'' spp.), pasto de agua (''Potamogeton pusillus''), reeds (''Scirpus'' or ''Typha'' spp.), and various species of the Asteraceae family.〔〔 It has significant biodiversity in its fauna but much is relatively unstudied.〔 Economic development in the 20th century has caused environmental problems, especially in the south of the valley. These include air and soil pollution from an important refinery and electric power plant near the city of Tula. The most serious problem comes from wastewater which is pumped into the area from the neighboring Valley of Mexico.〔 The wastewater comes from drainage projects that carry water out of the Valley of Mexico and dump it into the Tula River, with most of the water not treated adequately or not treated at all.〔〔 The wastewater is a mix of residential and industrial water, which includes contaminants such as bacteria (such as cholera) from fecal matter and toxic chemicals. This contamination is severe enough in places to be seen and smelled. Nevertheless, the water is an important source for irrigated farming, especially in the Tula and Alfajayucan areas, with the water "treated" by letting it soak through the soil. The water causes contamination of groundwater, including water that eventually becomes part of the Pánuco River, affecting coastal lagoons on the Gulf of Mexico.〔 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「Mezquital Valley」の詳細全文を読む スポンサード リンク
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