The Rio Ouro Preto Extractive Reserve is divided between the municipalities of Guajará-Mirim (73.45%) and Nova Mamoré (26.55%) in Rondônia.

[2] 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.

[3] The reserve occupies the basin of the Ouro Preto River between two parallel east-west ranges of hills.

[3] 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.

[4] On 5 September 2003 the Instituto Nacional de Colonização e Reforma Agrária recognised that the reserve had the capacity for 109 families with access to PRONAF support.

In the rainy season the river spills over its banks and floods the forest with dark water due to suspended organic matter.

Most of the soils have low agricultural potential apart from some areas of rich black earth that were created by pre-colonial indigenous farmers.

[4] The most economically valuable plants species are the Itaúba, Maçaranduba, Sorva, Caucho, Copaiba, Seringueira and Castanheira.

There are few areas of unflooded land near the rubber allotments, but these are planted with maize, rice, beans and other crops.