(grän chä'kō) or Chaco, c.250,000 sq mi (647,500 sq km), extensive lowland plain, central South America. It is sparsely populated and is divided among Paraguay, Bolivia, and Argentina. Some of the highest temperatures in the southern continent are reached there. To the north of the Pilcomayo River and to the west of the Paraguay River is the section known as the Chaco Boreal, which divided between Bolivia and Paraguay. This is arid land, dotted with swamps in the rainy season and with stretches of dense forest in which the quebracho tree abounds. Tannin extraction from the quebracho is an important economic activity there; large factories have been built for this purpose. In recent years cattle ranching has become an increasingly important industry, especially in Paraguary, leading to significant deforestation. The Chaco Central, in Argentina S of the Pilcomayo River and N of the Bermejo River, has much the same aspect. Cotton and quebracho are important there. Below the Bermejo, also…