A uniquely complete and continuous sequence of early Miocene through early Pleistocene marine sediments is exposed in Bonita Canyon on the western flank of the San Joaquin Hills and at adjacent Newport Bay, California. These sediments are assigned to the early to middle Miocene Topanga Formation, middle to late Miocene Monterey Shale, late Miocene to early Pliocene Capistrano Formation, and early Pliocene to early Pleistocene Fernando Formation. The total thickness of the sequence studied is more than 2,400 m.

Quantitative analysis of benthonic foraminiferal biofacies indicates that: (1) the lower parts of the Topanga Formation were deposited at inner to outer shelf depths, (2) upper Topanga and Monterey Shale diatomaceous sediments were deposited at upper to middle bathyal depths within a closed basin where ambient water contained less than 1 ml/l of dissolved oxygen, (3) lower bathyal depths marked by abundant radiolarian tests occurred during deposition of the Capistrano Formation, and (4) the Fernando Formation was deposited at lower bathyal through outer shelf depths. Stratigraphic variations of gross faunal parameters including foraminiferal number, radiolarian number, planktonic-benthonic ratio, and percent of displaced benthonic species provide additional quantitative evidence of th shelf-to-basin-to-shelf paleobathymetric history of this sequence. Ranges of individual species of benthonic Foraminifera allow the Saucesian, Relizian, Luisian, Mohnian, Repettian, Venturian, Wheelerian, and Hallian Stages to be recognized. Cool to warm temperate planktonic foraminiferal biofacies dominated by Globigerina concinna sl. and G. angustiumbilicata occur in the Topanga Formation and lower Monterey Shale. Temperate planktonic assemblages dominated by G. bulloides sl. dominate in the upper Monterey Shale and parts of the Fernando Formation. A subarctic biofacies containing sinistral populations of G. pachyderma is present at discrete intervals within late Miocene, middle and late Pliocene, and early Pleistocene sediments, whereas a subtropical-warm temperate biofacies dominate by Globoquadrina dutertrei is restricted to the early Pliocene. Ranges of critical planktonic Foraminifera including Globorotaloides trema, Globorotalia mayeri, G. menardi, G. crassaformis, G. inflata, G. truncatulinoides, "Orbulina universa," "Sphaeroidinella dehiscens," and the radiolarian Prunopyle titan provide additional criteria for age assignment and correlation with the paleomagnetic-radiometric time scale.

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