The Purus River rises in Peru. It defines the boundary between Peru and Brazil in the centre of the state of Acre, then runs for a short distance along the boundary of the 231,555 hectares (572,180 acres) Santa Rosa do Purus National Forest, a sustainable use conservation unit created in 2001 after it is joined by the Santa Rosa River. It then flows north east through Manoel Urbano[2] It runs through a continuous forest at the bottom of the great depression, lying between the Madeira River, which skirts the edge of the Brazilian sandstone plateau, and the Ucayali River, which hugs the base of the Andes.[citation needed]