Santa Rosa Canyon dissects the Sierra de Santa Rosa at the western end of an arcuate range in south-central Nuevo Leon, Mexico, about 40 km west of Linares. About 2,000 m of Late Jurassic (Tithonian) to Late Cretaceous (Maestrichtian) rocks are exposed. The Taraises Formation is composed mainly of dark gray to black, well-indurated lime wackestones and mudstones 132 m thick. The upper part of the formation includes 31 m of dark calcareous shale which contains a few thin beds of moderately indurated lime wackestone which bear ammonites of Valanginian age. Other megafossils are rare throughout the formation. Microfossils are common to abundant in about one third of the samples collected at 2-m intervals. Induration and recrystallization allowed micropaleontologic study by t in section only. The microfauna includes radiolarians, ostracods, echinoderm debris, and unidentified biogenic grains as well as calpionellids and nannoconids, but only the last two are persistently common.

Calpionellid taxa include Amphorellina subacuta Colom, Calpionella alpina Lorenz, Calpionella elliptica Cadisch, Calpionellites darderi (Colom), Calpionellopsis oblonga (Cadisch), Calpionellopsis simplex (Colom), Remaniella cadischiana Catalano, Salpingellina levantina Colom, Stenosemellopsis hispanica (Colom), Tintinnopsella carpathica Colom, and Tintinopsella longa (Colom). The distribution of these taxa indicates that the Taraises ranges in age from middle Berriasian to the Hauterivian-Valanginian boundary. No calpionellids were found in the overlying Tamaulipas (= La Pena and Cupido of many workers).

Although abundant in some thin sections, nannoconids were less useful than calpionellids. Nannoconus steinmanni Kamptner appears intermittently throughout the Taraises Formation. It has been reported to range throughout the Berriasian and Valanginian. Other species of nannoconids were tentatively identified but they are comparable in form and range and their occurrence was plotted with N. steinmanni.

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