Gran Chaco

Gran Chaco or Chaco, region, south central South America, covering about 647,500 sq km (250,000 sq mi), and encompassing part of Argentina, Paraguay, and Bolivia. The Chaco is conventionally divided into the Chaco Boreal (Northern Chaco), the largest division; the Chaco Central; and the Chaco Austral (Southern Chaco).

The Chaco is a low, flat, alluvial plain. It is generally hot and arid, but in the summer rainy season (December to April) it is subject to flooding by rivers that turn large parts into swamp. The chief rivers are the Pilcomayo and Bermejo, which cross the Chaco in a south-eastern direction from the Andean foothills towards the Paraguay and Paraná rivers, which are the only rivers of the region that are navigable for great distances. The hard clay that characterizes the soil aggravates the flooding and inhibits agriculture. Along the waterways in the east are tall reeds and palms; these give way inland to scrub forest and grassy savannah; in the west are dense growths of thorny brush and desolate arid stretches. Wildlife is abundant and includes jaguar, ocelot, tapir, anteater, capybara, peccary, and agouti. There are also many bird, reptile, and insect species. The savannah is used for cattle ranching, which, with cotton growing in the south, has been developed with some success since the 1930s. The forested part of the Chaco in Paraguay and northern Argentina is noted for timber, especially the red quebracho logs from which comes much of the world's supply of tannin.

Few roads and railways cross the area, which is sparsely populated. The principal settlements are Mariscal Estigarribia, a Paraguayan army post, and Filadelfia, a Mennonite colony, both in the Paraguayan Chaco Boreal; various Paraguayan ports on the western bank of the Paraguay River, the largest of which is Villa Hayes; and the Argentinian cities of Formosa and Resistencia. Disputes over boundaries between Bolivia and Paraguay led to armed conflict in the 1930s—the Chaco War.