A quantitative study was made of the microfossil and sedimentology of most of the Tertiary section in Tecolote Tunnel, Santa Barbara County, California. Foraminiferal evidence indicates that the Cozy Dell shale and Coldwater sandstone are middle Eocene bathyal deposits with an abundance of turbidites. A major middle Tertiary basinal cycle commenced in the Oligocene with the alluvial fan deposits of the Sespe Formation, giving way to middle bathyal deposits with turbidites in the upper Vaqueros Sandstone and Richon Shale formations, and finally to deeper-silled basin deposits in the Mohnian part of the Monterey Shale, also with turbidites. One planktonic foraminiferal zone is recognized for the middle Eocene, and 3 were established for the Miocene. Carbonate/nitrogen ratios were useful in selecting the division between the nonmarine Sespe Formation and the marine paralic facies of the basal Vaqueros Sandstone. The stages of the California Miocene are adjusted to the standard European section by evaluating the Orbulina universa datum.

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