An important late Miocene flora occurs in the diatomaceous shales of the Yorba Member of the Puente Formation in the Los Angeles Basin of southern California. The terrigenous plant assemblage includes both hard- and soft-wood species and consists of Taxodium dubium (Sternberg), Quercus conveza Lesquereux, Magnolia californica Lesquereux, Persea cf. P. psudocarolinensis Lesquereux, Platanus paucidentata Dorf, Ilex opacoides Condit, Acer bolanderi Lesquereux and Nyssa sp. aff. N. californica MacGinitie. Several species of diatoms also have been recognized: Annellus californicus Tempere, Coscinodiscus cf. C. lineatus Ehrenberg, C. radiatus Ehrenberg, Diploneis smithi (Brebisson) and Synedra nitzschioides Grunow.

      The composition of the Puente Flora suggests three climatic elements: a subtropical coastal lowland (including a swamp group and an associated swamp-border group), a subtropical protected upland canyon, and an exposed arid or semiarid upland.

      The suggested Late Miocene age for the Puente Flora is consistent with its general composition, and is apparently confirmed by the occurrence of Late Miocene (upper Mohnian) foraminifera.

      Geologic and paleontologic evidence suggest that terrigenous members of the flora were derived from the ancestral San Gabriel mountains of the northeast, and that the assemblage was deposited at a depth of at least 1800 feet, but less than four miles from shore.

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Presented at the 6 August 1970 meeting of the Southern California Paleontological Society, Los Angeles.

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