We examine the regularities of formation, development and transformation of geosystems of Cisbaikalia. Special attention is given to the influence of tectonic processes on the formation of landscape borders and transition zones of a high taxonomic level. We determined the formation stages of taiga geosystems of the region, demonstrated the main indicators of their transformation, the characteristics of transformation of geosystems at different taxonomic levels, and established the transformation trend of geosystems. Based on the identified regularities, we highlighted the areas undergoing disastrous transformations of geosystems. The findings are represented as a synthesis of data and knowledge concerning the territory, based on V.B. Sochava’s theory of geosystems, results from station-based and strip survey investigations, cartographic information, and on GIS technologies. The research presented can serve as a basis for working out the concept of the region’s sustainable development and environmental protection.