Summary Total EP Bolivie carried out two Magnetotellurics (MT) surveys in the bolivian fold belt of the sub-andean foothills. These surveys were aiming to estimate the local absolute depth of the Los Monos/Huamampampa (Devonian) resistivity interface at depth about 5-6 km, and map the relative geometry of this resistivity interface. To achieve this goal, MT was extensively analyzed with a dedicated workflow. First, data quality was assessed; then, the most up-to-date geological interpretation was introduced in sequential 2D/3D unconstrained & constrained inversions; the last step was the updated HMP interpretation from the results of 2D and 3D inversions. The foothills of Southern Bolivia are characterized by a succession of sub-parallel NS trending mountain ranges, which correspond to a tightly folded elongated anticline structure, predominantly composed of clastics sediments.