Rio de Janeiro | Rio Grande do Sul | Rio Grande | Rio de Janeiro (state) | Rio Grande do Norte | Río de la Plata | Rio | Rio Tinto Group | Rio Negro | Natal, Rio Grande do Norte | Rio Tinto | Rio Negro (Amazon) | Rio Grande Valley | Pinar del Río | Río Piedras, Puerto Rico | Rio Branco | Pinar del Río Province | Rio Ferdinand | Universidade Federal do Rio Grande do Sul | Río Negro | Del Rio, Texas | Rio Tinto Alcan | Río Piedras | Río Negro Province | Río Cuarto, Córdoba | Resende, Rio de Janeiro | Río Cuarto | Federal University of Rio de Janeiro | Santa Maria, Rio Grande do Sul | Rio Verde |
The region includes the Tuxtla Mountains and stretches from Laguna Alvarado, along the Gulf of Mexico, to Laguna del Ostión, then along the westernmost tributaries of Laguna del Ostión, to the northernmost tributaries of Río Coatzacoalcos, then along the Río San Juan to its merger with Río Papaloapan flowing into the Gulf of Mexico.