Potassium-argon age determinations on volcanic strata that overlie an extensive postorogenic erosion surface in the Western Cordillera show that the “Incaic pulse” of compressive deformation as well as subsequent uplift and erosion of the Andes of central Peru had taken place before 40 to 41 m.y. ago. Intense volcanic activity, which began before the end of uplift and erosion, continued for about 6 m.y. into early Oligocene time. The timing of these events suggests that uplift and volcanic activity, and perhaps also the preceding tectonic pulse, may have been initiated by the same global disturbance that produced the abrupt change in direction of movement of the Pacific lithospheric plate reflected by the bend in the Hawaiian-Emperor volcanic chain.