Abstract: The object of the study are ice-mineral permafrost mounds (lithalsas) in the valley of the Sentsa River in the Eastern Sayan Mountains (52º39.827' N, 99º29.858' E). The aim of the research is to study the internal structure of the mounds and, in particular, the depth of occurrence of ice lenses. The article examines the magnetic susceptibility of alluvial soils and entic podzols to determine the intensity of Fe illuvial process. The content of organic carbon and iron in soils was measured. Electromagnetic prospecting was performed using a symmetric four-electrode Schlumberger installation using a set of ASTRA-100 (generator) and MERI-24 (measuring instrument). The magnetic susceptibility of the soil was measured using a portable magnetic susceptibility meter PIMV-M over a uniform grid of 20 cm. The total content of Fe in soils was measured by ICP-MS. It was established that the ice lenses are located at depths of about 4 meters and have a vertical thickness of 10 meters. The presence of two separate ice lenses in the largest of the studied mounds was established. Magnetometry confirmed the high intensity of the Fe illuvial process in lithalsa soils. Ground squirrels inhabiting this area create places for the accumulation of iron compounds.