Structural analysis of remotely sensed images of Eritrea, guided by the common presence of a mid-Oligocene datum at the base of flood basalt at different elevations, helps to piece together the Tertiary history of the western flank of the Red Sea basin. Many of the Tertiary faults are reactivated shear zones in the Pan-African basement, the most important Tertiary fault at the foot of the Red Sea Escarpment marking the site of a pre-Tertiary boundary between andesitic island-arc crust and deeper, perhaps older granitoid migmatites. The initiation of extensional sedimentary basins in Eritrea clearly followed volcanism, as did doming and uplift. This sequence lends some support to active mantle upwelling as the primary tectonic impetus, specifically to massive melting simultaneous with plume impact with the lithosphere. The coincidence of major Tertiary extensional faults with zones of mid- crustal to lower- crustal silicic basement may indicate that active mantle processes were focused by zones of rheologically weak lithosphere, as postulated by Dixon et al. (1989).