Oriental Basin 1.38

The Oriental Basin, also known as the Libres-Oriental Basin, Oriental-Serdán Basin or San Juan Plains is an endorheic basin in east-central Mexico. It covers an area of 4,958.60 square kilometers, lying in the states of Puebla, Tlaxcala, and Veracruz.The climate is temperate and subtropical, semi-arid to subhumid, with summer rains. Average annual temperature 12-16 °C, and annual total precipitation is 400–800 mm. The Trans-Mexican Volcanic Belt pine-oak forests ecoregion covers the mountains surrounding the basin to the west, north, and east. The mountains to the north and west, including the Cofre de Perote volcano, leave the valley in a rain shadow, and the xeric shrublands of the Tehuacán Valley matorral ecoregion occupies the center of the basin, and extend south into the Tehuacán and Cuicatlán valleys. Vegetation includes pine-oak forests and pine-fir forests at higher elevations, with dry scrub pine forests, oak forests, juniper scrub, yucca scrub, halophytic vegetation, and grassland. It includes the Llanos de San Juan and Llanos de San Andres.The basin contains a several shallow, mostly alkaline lakes. Two ephemeral playa lakes, Totolcinco and Tepeyahualco, lie in the lowest part of the basin, and remain dry for most of the year. The basin includes six maar lakes, locally called axalpazcos, lying in shallow volcanic craters and sustained by underground water. A northern group of lakes – Alchichica, Quechulac, Atexcac, and La Preciosa – lie southeast of Lake Tepeyahualco, and the southern lakes, Aljojuca and San Miguel Tecuitlapa, lie southeast of Lake Totolcinco. The basin also has five dry maars, called xalapazcos.