The park sits in the Purus-Madeira interfluvial - the wedge of forest between two of the Amazon's great southern tributaries. The Matupiri River threads through the center, running from southwest to northeast, and it is the only practical way into the park's interior. To the southeast the protected area borders the Rio Madeira Sustainable Development Reserve. To the north it touches the Igapo-Acu Sustainable Development Reserve, which absorbs the impact of the BR-319 highway corridor. To the northeast it adjoins the Cunha-Sapucaia Indigenous Territory, where the Mura have been legally recognized since before the park existed. The geography is not arbitrary. Together, these protected areas form an ecological corridor across one of the most biodiverse and least studied regions of the Amazon basin - a stitched-together refuge for species that need room to move.

Ninety-one percent of the park is dense lowland rainforest with emergent canopy trees - the standard Amazon tall-tree biome. But the remaining seven percent is something unusual: grassy wooded savanna, called Amazon campina, without gallery forest. The campina exists in patches surrounded by rainforest, as if a piece of cerrado - the Brazilian savanna that dominates the country's center - had been dropped into the wrong biome. Nobody fully understands why. The soils seem to play a role; some campinas grow on sandy, nutrient-poor ground where taller trees cannot establish. Whatever the cause, the patches harbor species that exist nowhere else. Two possibly new fish species have been identified in the park's streams, along with three possibly new reptiles or amphibians, and six birds endemic to the narrow Purus-Madeira corridor. When park biologists began surveys, they were not cataloging known life. They were finding new kinds.

Amazonas state decree 28424, issued on March 27, 2009, created the park. A 2006 study that led to the decision had barely accounted for the Mura who lived along the Matupiri River. The study noted them mostly for what it called invading fishing lakes in the nearby Igapo-Acu reserve - language that reflected a bureaucratic blind spot. The Mura, for their part, argued they had been the historical protectors of the Matupiri basin, using its resources as generations of ancestors had. When state officials began formal monitoring in 2011, they found physical evidence supporting that claim: house structures, wood-working areas, the telltale secondary-growth vegetation of past clearings. The Mura had not been hypothetical inhabitants. They had been there the whole time, quietly managing a forest the planners had treated as empty.

For the Mura, the park is not wilderness. It is a multi-generational resource base. They cut wood here to build canoes and houses. They gather Brazil nuts when the capsules fall in the dry season, cracking them open with machetes. They harvest copaiba oil and andiroba oil - both of them valuable medicinal and craft materials - and the fruits of acai, buriti, bacaba, and patua palms, which yield juice, pulp, and cooking ingredients. They fish. They collect honey from stingless bee colonies. They have, for decades, worked as guides for sports fishermen who came up the Matupiri with rods and cooler boxes. When the park was created, that tourism revenue dropped by nearly half - the new protected status rattled operators who had been working in an unregulated zone. The losses hit the Mura as hard as anyone. Protection without consent can look a lot like dispossession.

Brazil had no legal precedent for allowing indigenous people to use the resources of a state park. Colombia and Peru had developed principles for similar situations. The Matupiri management plan, approved on July 22, 2014, adapted those principles into Brazilian law for the first time. It defined an Indigenous Special Use Zone - ZUEI, in the Portuguese acronym - covering the land along major rivers and streams upstream from the recognized Mura territory. Inside that zone, Mura traditional activities are protected. Outside it, stricter rules apply. The deal required admitting that the Mura had been here first, that their presence was not a problem to be managed, and that real conservation in the Amazon cannot be separated from the people who have lived with the forest longest. As of 2016, the park was supported by the Amazon Region Protected Areas Program. The experiment continues - contested, imperfect, ongoing.