The Paraneña region extends from the Río Paraguay eastward to the Río Paraná, which forms the border with Brazil and Argentina. The eastern hills and mountains, an extension of a plateau in southern Brazil, dominate the region, whose highest point is about 700 meters above sea level. The Paraneña region also has spacious plains, broad valleys, and lowlands. About 80 percent of the region is below 300 meters in elevation; the lowest elevation, 55 meters, is found in the extreme south at the confluence of the Río Paraguay and Río Paraná.
The Paraneña region is drained primarily by rivers that flow westward to the Río Paraguay, although some rivers flow eastward to the Río Paraná. Low-lying meadows, subject to floods, separate the eastern mountains from the Río Paraguay.
The Paraneña region as a whole naturally divides into five physiographic subregions: the Paraná Plateau, the Northern Upland, the Central Hill Belt, the Central Lowland, and the Ñeembucú Plain. In the east, the heavily wooded Paraná Plateau occupies one-third of the region and extends its full length from north to south and up to 145 kilometers westward from the Brazilian and Argentine borders. The Paraná Plateau's western edge is defined by an escarpment that descends from an elevation of about 460 meters in the north to about 180 meters at the subregion's southern extremity. The plateau slopes moderately to east and south, its remarkably uniform surface interrupted only by the narrow valleys carved by the westward-flowing tributaries of the Río Paraná.
The Northern Upland, the Central Hill Belt, and the Central Lowland constitute the lower terrain lying between the escarpment and the Río Paraguay. The first of these eroded extensions stretching westward of the Paraná Plateau--the Northern Upland-- occupies the portion northward from the Río Aquidabán to the Río Apa on the Brazilian border. For the most part it consists of a rolling plateau about 180 meters above sea level and 76 to 90 meters above the plain farther to the south. The Central Hill Belt encompasses the area in the vicinity of Asunción. Although nearly flat surfaces are not lacking in this subregion, the rolling terrain is extremely uneven. Small, isolated peaks are numerous, and it is here that the only lakes of any size are found. Between these two upland subregions is the Central Lowland, an area of low elevation and relief, sloping gently upward from the Río Paraguay toward the Paraná Plateau. The valleys of the Central Lowland's westward-flowing rivers are broad and shallow, and periodic flooding of their courses creates seasonal swamps. This subregion's most conspicuous features are its flat-topped hills, which project six to nine meters from the grassy plain. Thickly forested, these hills cover areas ranging from a hectare to several square kilometers. Apparently the weathered remnants of rock related to geological formations farther to the east, these hills are called islas de monte (mountain islands), and their margins are known as costas (coasts).
The remaining subregion--the Ñeembucú Plain--is in the southwest corner of the Paraneña region. This alluvial flatland has a slight westerly-southwesterly slope obscured by gentle undulations. The Río Tebicuary--a major tributary of the Río Paraguay -- bisects the swampy lowland, which is broken in its central portion by rounded swells of land up to three meters in height.
The main orographic features of the Paraneña region include the Cordillera de Amambay, the Cordillera de Mbaracayú, and the Cordillera de Caaguazú. The Cordillera de Amambay extends from the northeast corner of the region south and slightly east along the Brazilian border. The average height of the mountains is 400 meters above sea level, although the highest point reaches 700 meters. The main chain is 200 kilometers long and has smaller branches that extend to the west and die out along the banks of the Río Paraguay in the Northern Upland.
The Cordillera de Amambay merges with the Cordillera de Mbaracayú, which reaches eastward 120 kilometers to the Río Paraná. The average height of this mountain chain is 200 meters; the highest point of the chain, 500 meters, is within Brazilian territory. The Río Paraná forms the Salto del Guairá waterfall where it cuts through the mountains of the Cordillera de Mbaracayú to enter Paraguayan territory.
The Cordillera de Caaguazú rises where the other two main mountain ranges meet and extends south, with an average height of 400 meters. Its highest point is Cerro de San Joaquín, which reaches 500 meters above sea level. This chain is not a continuous massif but is interrupted by hills and undulations covered with forests and meadows. The Cordillera de Caaguazú reaches westward from the Paraná Plateau into the Central Hill Belt.
A lesser mountain chain, the Serranía de Mbaracayú, also rises at the point where the Cordillera de Amambay and Cordillera de Mbaracayú meet. The Serranía de Mbaracayú extends east and then south to parallel the Río Paraná; the mountain chain has an average height of 500 meters.
Data as of December 1988