Abstract: The research objects are permafrost sediments and frost mounds in the Sentsa river valley. The problem of their formation in the alluvium period attracts the attention of many scholars in different fields of study (from geo-botanists to specialists in geo-cryology). The complex pilot studies included boreholes drilling, detailed documentation of frost borehole samples, penetrated sections of frost mounds, and river terrace cusps, tacheometric survey of the Sentsa river valley, GPS-anchoring of reference sections and boreholes, defining the ice content (humidity), and the lithological, grain-size and microaggregate composition of lacustrine-alluvial sediments. The analysis has been performed by the specialists of the shared knowledge center “Geodynamics and geochronology” (the Institute of the Earth’s Crust of the Siberian Branch of the Russian Academy of Sciences, Irkutsk) using the modern methods. The authors conclude that frost mounds consist mainly of silt loams with the interlayers of heavy clay sand and ice lenses (up to 0,65 m). Cryo-textures are fissile, crossbedded, thick-schlier, wide-meshed, basal. The designed 3D model of the relief speaks for the presence of either a vast area with many frost mounds of different sizes, or of one gigantic mound, which at the present time is defragmented due to active thermokarst on a terrace above the flood-plain and thermoerosion of the sides of the Sentsa river. According to the preliminary data, frost mounds are cryogenic formations of a mixed segregation-intrusive genesis. The final goal of the research is the elaboration of a scenario of formation of permafrost lacustrine-alluvial sediments and the creation of a theoretic model of the Holocene evolution of frost mounds of the Oka plateau.