The San Francisco Bay basin in central coastal California has formed in response to the capture by and emplacement onto the Pacific plate of the Salinian terrane during the past 4 m.y. The addition of mass (the Salinian terrane) onto the Pacific plate caused the flexural downwarp of the Pacific plate and the formation and subsidence of the San Francisco Bay basin. As a result of continued plate-boundary evolution, sedimentary basins that previously formed in this way along the San Andreas fault may be ephemeral. Much of the basin may be removed during crustal capture by the Pacific plate and translation through Santa Cruz Mountain–like fault geometries. Remnants of such flexural downwarp basins may be preserved within the nearshore basins on the Pacific plate.