CHACO, Er, GRAN. A name applied to a re gion of central South America extending north v,ard from the Salado Biver to about latitude 18' S., and included between the Paraguay and Parana rivers on the east and the foot: hills of the Andes on the west. It thus comprises large part of northern Argentina and western Paraguay. and smaller portions of southeastern Bolivia and southwestern Brazil. The Chaco Boreal includes the section north of the Pil omayo; the Chaco Central, the between the Pileomayo mid the Bermejo: and the Chaco Austral, the section south of the latter river. The region is a vast plain, undulating in places, but for the most part flat, and sloping gently toward the southeast. Its mean elevation ranges from about 1000 feet on the western edge to 100 feet on the east. The large rivers which cross the Gran Chaco are subject to periodieat freshets, and inundate vast areas of the low lying ground. With the subsidence of the Ara tera, 1111111er011ti lakes and swamps are formed which may remain for a greater part of the year. These lowlands arc covered with heavy forests, and with thickets of vines and bushes, while the more elevated areas support. a luxuri
ant growth of grasses. A large part of the re gion lies within the great Tertiary basin of South America. and has a sandy or clayey soil. The climate is generally hot, except in the win ter months, and the daily range of temperature is extreme. The rainfall is rather low, the heavi est precipitation occurring in summer. Except on the borders, the entire area is uncultivated and thinly populated. A few nomadic and sav age Indian tribes live in the interior, and have resisted all attempts of the various governments toward their civilization. The hostility of the Indians and the dense, matted growth of vegeta tion along the streams have been serious ob stacles to the exploration of the Gran Chaco. In the last few years Argentina and Bolivia have undertaken the exploration and develop ment of parts of the region, and this work doubt less will be continued in the future. See ARGEN TINA; BOLIVIA; PARAGUAY.