The Cerdanya basin was formed during dextral slip along the NE–SW La Tet fault (eastern Pyrenees) which formed a horsetail structure at its SW end. The resulting basin is clearly asymmetrical, formed by several basement blocks tilted towards the La Tet fault and limited by E–W faults. These faults absorbed the movement along the major strike-slip fault. The early basin evolution (Middle–Late Miocene) resulted from strike-slip, while the later evolution (Early Pliocene) involved a generally extensional regime.
A variety of depositional environments developed in the basin during its early evolution: spatially restricted and widespread alluvial fan, distributary fluvial, marginal and open lacustrine. The structural features of the basin that developed during this evolutionary stage differ from those described from most other basins related to strike-slip faulting. Despite this, the structural and sedimentary features of the Cerdanya basin fit the general model of strike-slip related basins.