the study of cross-cultural processes in the colonial frontiers in latin america shows keys to explain the dynamics of interethnic relationships, acculturation experiences and construction of identities. likewise, the functioning of the colonial order can be analyzed from the ways the power relationships were structured in the areas where the aborigines preserved autonomy and crontrol of their territories and resources. hispanic-native relationships are studied from this theoretical point of view, in one of the last borders where the hispanic expansion got since the bourbon's duty imposed, that is the southernmost territories of río de la plata. analyzing the ways of interaction in the río negro fortress, we identified the hispanic-local and aboriginal strategies and recognize the stabilization of a transaction assemblage that defined a special regime of interchanges based on reciprocity. these political and economic practices favoured the maintenance of certain balance of forces, which is shown in the decrease of frontier struggle during the last decades of the colonial period.