Claim: The Chapada das Mangabeiras is a mountain range that runs northwest-southeast and  forms the boundary between Tocantins state and the states of Maranhão and Piauí.
Evidence: The range runs northwest-southeast, and separates the basin of the Tocantins River to the southwest from the upper basin of the Parnaiba River to the northeast. The range also forms the boundary between Tocantins state and the states of Maranhão and Piauí.