Objective/Context: This article explains how the Sierra de La Macarena Biological Reserve, which marked the beginning of the new state responsibility of caring for nature in Colombia, was conceived and then created by law in 1948. Additionally, this paper reconstructs the first decade of its existence. Methodology: This research is based on archival documents, historic publications and secondary sources, which allow us to understand the ideas about nature that guided such history and the concrete processes that characterized it. Originality: This article studies the process of State formation from a territorial and environmental perspective, bringing together political and environmental history, and pointing at new avenues of inquiry in both fields. Conclusions: The beginnings of a new state responsibility of caring for nature depended on previous developments of the state itself, particularly on the efforts to deal with tropical diseases. Therefore, an area of state activity devoted to insure the well-being of the population served as the basis for the inceptive development of another. This issue was, however, not entirely national. Global scientific networks, including medical doctors, entomologists and geologists, together with an innovative technology, aviation, also played a crucial role. The research station that was conceived along with the reserve to support long-term research was partly impaired by La Violencia of the 1950s. Instead, scientists carried out several expeditions that contributed to turn La Macarena into national patrimony, at least in the minds of some Colombians. Given that aspirations well exceeded the achievements, the definitive emergence of this area of state performance had to wait a few years. [ABSTRACT FROM AUTHOR]