The study is devoted to the search for illegal sand mining in the Republic of Mari El, which causes irreparable damage to the environment and requires significant labor costs for their search and detection in the forest zone. The relevance of the study is on ever-growing technogenic impact on the geological environment. We analyzed high-resolution remote sensing images to identify changes in subsoil areas. The database which ensures monitoring of subsoil use in the territory of the Republic of Mari El was updated and actualized. Space imagery monitoring was based on space images of Resource-P and Canopus-B for 2017– 2018 coverage of the territory of the Republic with satellite images suitable for decoding. The study revealed more than 100 subsoil use objects, among which 21 illegal quarries were confirmed during field verification. The main decryp-tion features of the quarries were formed. The chosen methodology can be used in the future for ecological environmental monitoring in the regions of the Russian Federation. The economic feasibility of the proposed methodology is on cutting material and labor costs spent on detection of illegal quarries. © 2021, Univelt Inc. All rights reserved.