It is isolated from other regions by the seasonally flooded várzea forest along these rivers, and has a high degree of endemism among its flora and fauna.

The Purus-Madeira moist forests ecoregion lies to the east of the Carauari arch, an ancient uplift zone in Brazil.

The plain holds large meandering rivers that have formed many oxbow lakes, and a great many small streams, all subject to annual flooding.

It is within the low Amazon Basin, an area of soft sediments that emerged from five to two million years ago.

[3] As with other forests of the Amazon basin the main families are Fabaceae, Sapotaceae, Lecythidaceae, Moraceae, Chrysobalanaceae, Lauraceae and Myristicaceae.

Four common species of palm are Astrocaryum vulgare, Oenocarpus bataua, Attalea maripa, and Socratea exorrhiza.

Other mammals include Hoffmann's two-toed sloth (Choloepus hoffmanni), brown-throated sloth (Bradypus variegatus), silky anteater (Cyclopes didactylus), southern tamandua (Tamandua tetradactyla), giant anteater (Myrmecophaga tridactyla), collared peccary (Pecari tajacu), jaguar (Panthera onca), cougar (Puma concolor), red brocket (Mazama americana), gray brocket (Mazama gouazoubira), and South American tapir (Tapirus terrestris).

[3] Endangered birds include wattled curassow (Crax globulosa) and red-necked aracari (Pteroglossus bitorquatus).

A paved road (BR-319) was built along the length of the region from Humaitá to Manaus, but it proved impossible to maintain and was closed.

The Trans-Amazonian Highway crosses the southwestern end of the region from Humaitá to Lábrea and has caused deforestation to create pasturage and agricultural fields.

[6] Global warming will force tropical species to migrate uphill to find areas with suitable temperature and rainfall.