Miocene floras from Fingerrock Wash, southwestern Nevada

Two floras of Miocene age, the Fingerrock and Stewart Spring, are found in a stratigraphic section that also contains fossil mammals. The Fingerrock flora occurs in beds below the Stewart Spring local fauna of transitional HemingfordianBarstovian (middle-late Miocene) age, and the Stewart Spring flora occurs above that fauna but below the Cedar Mountain local fauna of Cerrotejonian (earliest Pliocene) age.

The late Hemingfordian Fingerrock flora was dominated by the live oak, Quercus chrysolepis, but most of the flora is composed of species found in contemporaneous floras of the Columbia Plateau. These species include lobed Quercus, Carya, Ulmus, Zelkova, Platamis, and Acer. The lack here of certain other species found in this association to the north indicates that the Fingerrock flora lived in a drier climate than prevailed at the same time on the Columbia Plateau. Nevertheless the Fingerrock flora was a warm-temperate mesophytic flora. Twenty-four species are described from the Fingerrock flora, none of which are new.

The early, or more probably middle, Barstovian Stewart Spring flora is, besides the expected lacustrine element, dominated by Quercus chrysolepis, Picea breweriana, and Chamaecyparis nootkatensis. This assemblage is typically found only in western Nevada and is further restricted to floras of Barstovian and Clarendonian age. Most of the species in the Stewart Spring flora appear to be descended from northern mesophytic forms, although the flora has a subhumid aspect different from the northern floras. Only a small element in the Stewart Spring flora may contain species of southern origin. Several phylads in the Stewart Spring flora are now found on the margins of and in the Great Basin. The Stewart Spring flora contains 42 described species, 9 of which are new.