The Early Miocene Mohawk Valley Flora of the Northern Sierra Nevada contains well-preserved leaves, fruits, seeds and wood allowing for a detailed environmental interpretation. This fills a gap in our knowledge of the Tertiary flora of Western North America. Preliminary identifications include the first clear reports of Staphylea and Zanthoxylum in the Miocene flora of California. Previously recognized floras from this elevation and area of the Sierra Nevada are little studied, depauperate, dominated by leaves and/or unpublished. The Mohawk Valley Flora occurs at two localities in fluvial and lacustrine environments in the lowest member of the Bonta Formation [18.1 (+/- 2 - 3) Ma to 22.8 (+/- 1.6) Ma]. Little detailed mapping has been done in this area; ongoing fieldwork will provide local stratigraphic framework. Paleoclimatic interpretations will be based upon the Nearest Living Relative Method and the Climate-leaf Analysis Multivariate Program (CLAMP). While both methods have limitations, the combination of the two will (a) allow each to check the other and (b) allow interpretation of the overall climatic conditions at the time of deposition. The floristic affinities lie with present-day floras of the southeastern United States and warm-temperate eastern Asia, indicating a warmer, wetter environment than currently occurs in present-day Sierra Nevada. The Mohawk Valley Flora may represent an upland tongue of mesic vegetation linked to more northerly mixed mesophytic paleofloras. Paleofloras east and southwest of the Mohawk site suggest warmer, drier habitats. Full interpretation of the climatic setting may permit the interpretation of paleoelevation using leaf physiognomy and stomatal densities.

Key words: paleoclimate, paleoecology, paleoflora, Sierra Nevada