North of the State lies the Southern Plateau, formed by basaltic rocks originated by a great spill of lava occurred during the Mesozoic era. Its west end is the result of differential erosion, being named as Cuesta do Haedo. The highest altitudes of the Plateau are in the northeast, reaching 1,398 m in Monte Negro, located in São José dos Ausentes municipality. Its edges form Serra Geral.
At the center of the State there is the Central Depression, formed by sedimentary rocks that give origin a long corridor that links west to east, through low-lying lands.
At south lies the Sul-Riograndense Crystal Shield, formed by igneous rocks of the Precambrian period and, due to this, intensely worn by erosion. Its altitude does not exceed 600 m.
The Coastal Plain was formed in the Quaternary period of the Cenozoic era, the most recent one in the formation of Earth. It corresponds to a sandy strip of 622 km, with high occurrence of lagoons and lakes, among which stand out Patos Lagoon and Mirim Lake. The process of formation of this region has an evolutionary character, being in constant change, as a result of marine and fluvial-lacustrine sedimentation.