The Rio Ouro Preto Extractive Reserve is divided between the municipalities of
Guajará-Mirim (73.45%) and
Nova Mamoré (26.55%) in Rondônia. It has an area of . The
BR-421 federal highway runs east from the town of Guajará-Mirim on the Bolivian border, and enters the north part of the reserve. The reserve occupies the basin of the
Ouro Preto River between two parallel east-west ranges of hills. It extends westward along the course of the Ouro Preto to where it joins the
Pacaás Novos River, which forms the western boundary of the reserve. Altitudes range from above sea level. The reserve is part of the largest block of environmentally protected land in the state, and forms a buffer between the cleared and farmed areas and the strictly protected forest areas. The
Guajará-Mirim State Park lies to the north of the eastern part of the extractive reserve, the
Rio Ouro Preto Biological Reserve lies in the hills to the south of the eastern part, and the
Rio Pacaás Novos Extractive Reserve lies to the south of the western part. ==History==