Aeromagnetic and gravimetric studies made in the region of the Diois and Baronnies mountains (French Prealps) indicate a clear relation between deep structure and many surface structures. In particular, the basement took part in three displacements, the two great north-south faults of Saillans-Merindol and Die-la Motte-Chalancon, and the northeast-trending Clery fault. On the other hand, the east-west folds affecting the Mesozoic and Tertiary are definitely shallow decollements in which the basement did not participate.