Current radiometric dates of minerals in marine Neogene strata in California suggest a revision of the correlation between classic biostratigraphic units and the radiometric scale. The base of the lower Miocene corresponds approximately with the base of the Saucesian Stage, and it is dated at about 24.5 m.y.; the base of the middle Miocene is within the lower Relizian Stage, and, by extrapolation, it is slightly older than 19 m.y.; the base of the upper Miocene is equated with the base of the Mohnian Stage (the Globigerina pachyderma datum), and, again by extrapolation, it is no older than about 14 m.y.; the Miocene-Pliocene boundary is no older than about 9 m.y. and coincides approximately with the boundary between the Delmontian and Repettian Stages; the Pliocene-Pleistocene boundary is at least as old as 3 m.y.; and the Pleistocene-Holocene boundary is about 11,000 years B.P.