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Geography

The Gran Chaco is about 647,500 km (250,000 sq mi) in size, though estimates differ. It is located west of the Paraguay River and east of the Andes, and is mostly an alluvial sedimentary plain shared among Paraguay, Bolivia, and Argentina. It stretches from about 17 to 33°S latitude and between 65 and 60°W longitude, though estimates differ.

Historically, the Chaco has been divided in three main parts: the Chaco Austral or Southern Chaco, south of the Bermejo River and inside Argentinian territory, blending into the Pampa region in its southernmost end; the Chaco Central or Central Chaco between the Bermejo and the Pilcomayo River to the north, also now in Argentinian territory; and the Chaco Boreal or Northern Chaco, north of the Pilcomayo up to the Brazilian Pantanal, inside Paraguayan territory and sharing some area with Bolivia.

Locals sometimes divide it today by the political borders, giving rise to the terms Argentinian Chaco, Paraguayan Chaco, and Bolivian Chaco. (Inside Paraguay, people sometimes use the expression Central Chaco for the area roughly in the middle of the Chaco Boreal, where Mennonite colonies are established.)

The Chaco Boreal may be divided in two: closer to the mountains in the west, the Alto Chaco (Upper Chaco), sometimes known as Chaco Seco (or Dry Chaco), is very dry and sparsely vegetated. To the east, less arid conditions combined with favorable soil characteristics permit a seasonally dry higher-growth thorn tree forest, and further east still higher rainfall combined with improperly drained lowland soils result in a somewhat swampy plain called the Bajo Chaco (Lower Chaco), sometimes known as Chaco Húmedo (Humid Chaco). It has a more open savanna vegetation consisting of palm trees, quebracho trees, and tropical high-grass areas, with a wealth of insects. The landscape is mostly flat and slopes at a 0.004-degree gradient to the east. This area is also one of the distinct physiographic provinces of the Parana-Paraguay Plain division.

The areas more hospitable to development are along the Paraguay, Bermejo, and Pilcomayo Rivers. It is a great source of timber and tannin, which is derived from the native quebracho tree. Special tannin factories have been constructed there. The wood of the palo santo from the Central Chaco is the source of oil of guaiac (a fragrance for soap). Paraguay also cultivates mate in the lower part of the Chaco.

Large tracts of the central and northern Chaco have high soil fertility, sandy alluvial soils with elevated levels of phosphorus, and a topography that is favorable for agricultural development. Other aspects are challenging for farming: a semiarid to semihumid climate (600–1300 mm annual rainfall) with a six-month dry season and sufficient fresh groundwater restricted to roughly one-third of the region, two-thirds being without groundwater or with groundwater of high salinity. Soils are generally erosion-prone once the forest has been cleared. In the central and northern Paraguay Chaco, occasional dust storms have caused major topsoil loss.