Landforms present in this region include the upland terra firme (non-flooded) mostly on nutrient-poor lateritic soils, ancient alluvial plains (mostly non-flooded) on nutrient-rich soils, and present alluvial plains (várzea, seasonally flooded) of super-rich sediments renewed with each annual flood [REF].
The ecoregion contains stretches of Iquitos várzea along the main rivers, blending into Purus várzea near the eastern border, where it adjoins the Juruá-Purus moist forests ecoregion.