The magnetotelluric signature of the Alpine part of the Cantabrian Mountains was investigated in a N-S magnetotelluric profile, from the Duero basin to the Cantabrian shoreline. A two-dimensional conductivity model was obtained from the joint inversion of TM, TE modes and the geomagnetic transfer functions. A shallow conductor associated with the sediments of the Duero basin, and three north-dipping conductors in the upper and middle crust were detected. Of the latter, one is interpreted as the sole detachment of the Cantabrian Mountains, whereas the others correlate with the Cabu¿rniga and San Vicente de la Barquera faults. This geometry suggests that the Cantabrian Mountains comprise uplifted Variscan basement. A comparison with a seismic reflection profile shows a good correlation between these conductors and seismic features. The lower crust is characterized by high conductivities. ¿ 2001 American Geophysical Union