Abstract
The predominate Tertiary (44.2 ± 2.2 m.y.) intrusions of the Sacramento Mountains are thin dikes and sills of fine- and coarse-grained camptonite. Both rock types contain phenocrysts of diopsidic augite, hornblende, and plagioclase () in a fine groundmass of plagioclase (), chlorite, orthoclase, magnetite, and minor apatite. The rocks differ in that the coarse-grained camptonites have more mafic phenocrysts and the phenocrysts are larger (max. size 30 mm vs. max. size 12 mm). These mineralogical and textural differences are the result of flow differentiation. The coarser-grained camptonites formed during high magma discharge from the magma chamber and the finer-grained camptonites during low discharge.
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