We present the results of numerical simulations of Cenozoic volcanism in the Coast Ranges of California, associated with the northward migration of the Mendocino Triple Junction (MTJ). Three aspects of the thermal evolution and magmatism in the wake of the MTJ are investigated: (1) mantle flow and thermal perturbation in the ''slabless window''; (2) pressure-release partial melting in the upwelling asthenosphere; and (3) thermally induced crustal anatexis. Numerical results show that upwelling of asthenosphere in the ''slabless window'' causes a drastic change in the thermal structure of the lithosphere and results in significant pressure-release partial melting in the upwelling asthenosphere. Up to 4-5 km of basaltic magma may be produced. Most of this mafic magma is likely stored near the base of the crust. Thermally induced crustal anatexis mainly occurs in the deep crust (below 20 km), where a high degree (≥50%) of partial melting may be predicted. Most of the crustal melt is probably generated within 1 m.y. after the passage of the MTJ. This work also suggests that the spatial and temporal distribution of Cenozoic volcanism in the California Coastal Ranges is directly related to the variation of the relative velocity between the North America and Pacific plates in the last 30 m.y. The voluminous volcanic rocks in the northern California Coast Ranges correlate to the relatively high velocity between these two plates in the last 10 m.y. The reduced volcanism in the central Coast Ranges may be related to the slow migration of the MTJ between 10 and 20 Ma. ¿ American Geophysical Union 1992