In the Owens Valley region of California, volcanic activity of Cenozoic age was confined mainly to three areas near the ends of important faults. The volcanic eruptions seemingly took place in regions of relative tension, if the horizontal movement along these faults was left lateral. The deep depression of Owens Valley may have resulted from compression associated with left-lateral horizontal fault movement. The transfer of molten rock from beneath this deep depression laterally into the regions of tension and thence to the surface seems to account for the relief of abnormal stresses and the volume of the volcanic rocks.