Resumo. “Campinaranas” are sandy ecosystems of great extension in the Brazilian Amazon, and are determinant for the great systems of rivers with black waters. Due to the lack of studies on this ecosystem, the objective of the present work was to study the distribution of “Campinaranas” and their relationship with the predominant soils and geology in the western portion of the Brazilian Amazon. We used geographic data of vegetation, geology and soils, and analytical data of the soil profiles collected by the RADAMBRASIL project, updated and systematized by IBGE, and data from reference profiles collected in the National Park of Viruá,Roraima. In general, the soils of “Campinaranas” are predominantly sandy, developed on parent materials rich in quartz. The overlaying of geological data with areas dominated by “Campinaranas”, reveals the prevalence of recent sedimentary formations (Quaternary), constituted mainly of sandy materials. Based on the studied dataset, we suggest a minimum limit of 55 dag kg-1 of sand in the soils for the occurrence of “Campinaranas”. Soils with higher clay content are present only in Forest-Campinaranas transitions, adjacent to the sandy deposits. It is verified the absolute prevalence of Spodosols and Psamments in “Campinaranas”. Even in different geological formations and under distinct pedogenetic processes, these soils possess similar morphological, chemical and physical properties. In spite of the pedological diversity found in the transitional areas, the soils keep similarities with the soils of “Campinaranas”.