During the evolution of the Las Cañadas volcanic edifice, debris avalanches were very significant destructive events. The Roques de Garcia unit was generated by such an event. 39Ar/40Ar dating has been carried out on different rock types related to this deposit. 1.70-1.40 Ma ages were measured on volcanic matérial involved in the avalanche deposit, 0.43 Ma on a phonolitic dyke cutting this formation. These results bracket the age of the debris avalanche emplacement which could mark either the transition between Cañadas ll-Cañadas III (1.4-1.1 Ma) or Cañadas Illa-Cañadas lllb (0.6-0.7 Ma) volcanic phases