Calcareous nannoplankton are abundant in some rocks assigned to the California microfaunal stages. Most species are stratigraphically long ranging, although some have restricted stratigraphic ranges in low-latitude tropical regions. These species permit partial correlation of the California stages with the widely recognized plankton biostratigraphic zones of the tropics.

The upper Zemorrian is correlative with the Sphenolithus distentus through the lower Triquetrorhabdulus carinatus (NP 24-NN1) zones (upper Oligocene) the Saucesian with the upper T. carinatus through the lower Helicopontosphaera ampliaperta (NN1-4) zones (lower Miocene), the Relizian with the upper H. ampliaperta through the lower S. heteromorphus (NN4-5) zones (lower-middle Miocene), the Luisian with the upper S. heteromorphus through Discoaster kugleri (NN5-7) zones (middle Miocene), and the Mohnian with the Catinaster coalitus through D. calcaris (NN8-10) zones (middle-upper Miocene).

The species diversity of nannofossils in the California Oligocene-Miocene rocks is low. Like the planktonic Foraminifera from the same rocks, the nannofossils are analogous to species now living in the modern transitional water mass off California. There are no elaborate species as in the tropics and the floras tend to be dominated by single species (i.e., Coccolithus). These observations indicate that California was under the influence of a current flowing southward, with velocities nearly that of the modern California Current. The dominance of the assemblages by a single species, as well as other evidence from the rocks, indicates that upwelling was likely as important during the Miocene as it is today.

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