This article contains recent interpretations of the structural and tectonic evolution and the history of geological development of areas of Baikalian Siberia in the southern part of the Irkutsk amphitheater. We discuss the step-by-step formation of the largest structures on the Siberian platform’s surface, particularly those structures that are most important for defining contemporary geomorphological regions. The dominant role of tectonics in the geologic record of our region is stated. The modern river system represented by the Angara and its tributaries is rather young. It was formed during the last neotectonic sub-stage according to zones of tectonic faults. This river system was affected by tectonic ruptural deformations that occurred as a result of neotectonic activities.