[3] The north of the ecoregion reaches into the quartzite or sandstone upland terraces and mountains of the ancient Guiana Shield, while the south is in the much newer sedimentary basin of the Amazon River, formed during the recent Tertiary period.

The ecoregion is crossed by various blackwater or clearwater rivers, including the Trombetas, Jari, Uatumã, Curuapanema, Paru and Araguari.

There are areas of seasonal forest east of Óbidos that is dry in the summer and has a canopy under 20 metres (66 ft), with mesophyllous, semideciduous and xeromorphic flora.

[2] In the west, Manaus may be a region where organisms that had separated and evolved independently during ice ages came back together in warmer periods.

The forests to the north and east of Manaus are among the most diverse in the world, and include many endemic plants, animals and insects.

The most common families of trees are Sapotaceae, Lecythidaceae, Burseraceae, Fabaceae, Rubiaceae, Chrysobalanaceae, Lauraceae, Annonaceae, Moraceae, Mimosoideae and Caesalpinioideae.

[2] The dry hills to the north of Óbidos hold plants such as Zamia lecointei, Cynometra longifolia, Tachigalia grandiflora, Swartzia duckei, Ormosia cuneata, Peltogyne paradoxa, Cusparia trombetensis, Vochysia mapuerae, Bonnetia dinizii, Lacunaria sampaioi, Lophostoma dinizii, Ctenardisia speciosa, Mostuea brasiliensis, Macairea viscosa, Buchenavia corrugata, Ferdinandusa cordata, Pouteria speciosa and Lepidocordia punctata.

Other mammals include jaguar (Panthera onca), cougar (Puma concolor), anteaters, opossums and many rodents.

[2] Endangered mammals include the black bearded saki (Chiropotes satanas), pied tamarin (Saguinus bicolor) and giant otter (Pteronura brasiliensis).

[2] The habitat is fairly intact in the interior, but continues to suffer from deforestation along the main roads and rivers, around and to the north of Manaus, and in the region from Óbidos to Monte Alegre along the Amazon.

Cattle ranchers have cleared large areas of forest, as have commercial plantations around the Jari River and forestry in the east of the region.