lava plateau, one of the world's largest, southern Brazil. It lies mostly in Rio Grande do Sul and São Paulo estados (states), but it also spans parts of Santa Catarina and Paraná states. It is part of the Brazilian Highlands. Its formations of solidified sheets of lava rock (diabase) also appear in Uruguay, Argentina, and Paraguay. Where the diabase is exposed at the surface, it weathers into a well-drained, dark purple soil known as terra roxa, famous as a producer of coffee. Other crops grown there include feijão (beans), corn (maize), rice, cotton, and potatoes. The plateau is dissected by rivers, between which the surface is flat-topped.