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Coahuila, formally Coahuila de Zaragoza is one of Mexico's 31 component states. It is located in the north of the country. To the north, Coahuila accounts for a 512 kilometers (318 mi) stretch of the U.S. - Mexico border, adjacent to the U.S. state of Texas along the course of the Rio Grande (Río Bravo del Norte). Coahuila also borders the Mexican states of Nuevo León to the east, Zacatecas and San Luis Potosi to the south, and Durango and Chihuahua to the west. With an area of 151,571 square kilometers (58,521.9 sq mi), it is the nation's third-largest state.

The Sierra Madre Oriental runs northwest to southeast through the state, and the higher elevations are home to the Sierra Madre Oriental pine-oak forests.

East of the range, the land slopes gently toward the Rio Grande, and is drained by several rivers, including the Salado and its tributary the Sabinas. The Tamaulipan mezquital, a dry shrubland ecoregion, occupies the western portion of the state, and extends across the Rio Grande into southern Texas.

The portion of the state west of the Sierra Madre Oriental lies on the Mexican Plateau, and is part of the Chihuahuan Desert. The Bolsón de Mapimí is a large endorheic basin which covers much of the western portion of the state and extends into adjacent portions of Chihuahua, Durango, and Zacatecas. The Nazas River, which flows east from Durango, and the Aguanaval River, which flows north from Zacatecas, empty into lakes in the Bolsón. Torreón, the most populous city in the state, lies on the Nazas in the irrigated Laguna Region, the (Comarca Lagunera), which straddles the border of Coahuila and Durango.

The state contains two biosphere reserves. Maderas del Carmen lies on the northern border of the state, and includes sections of the Chihuahuan desert and sky islands of pine-oak forest in the Sierra del Carmen. The springs, lakes, and wetlands of Cuatro Ciénegas lie west of Monclova on the west slope of the Sierra Madre. The state is largely arid or semi-arid, but the rivers of the state support extensive irrigated agriculture, particularly cotton. The Parras district in the southern part of the state produces wines and brandies. The pine-oak forests of the Sierra Madre produce timber.