Axelrod: The Pliocene Verdi Flora of Western Nevada 93 



one of the easterly scarps of the Sierra Nevada, towers 3,500 feet above the valley 

 3 miles west of the locality. As discussed below, the Truckee River valley in the 

 Verdi area is a structural depression, formed by folding and faulting that have 

 been in operation intermittently through most of Late Cenozoic time. 



The valley area lies in the transition from pinon- juniper woodland to the Sierran 

 conifer forest. Scattered pinon (Pinus monophylla) and juniper (Juniperus 

 utahensis) occur just southeast of the fossil locality, and presumably were more 

 abundant over the lowlands prior to clearing for agricultural purposes. The 

 dominant shrub in the valley is Basin sage (Artemisia tridentata) , associated with 

 curl leaf mahogany (Cercocarpus ledifolius), rabbit brush (Chrysothamnus 

 nauseosus), desert peach (Primus andcrsonii), antelope brush (Purshia tri- 

 dentata), plateau gooseberry (Ribes velutinum), and horsebrush (Tetradymia 

 glabrata). With a slight rise in altitude the Sierran forest quickly takes over as 

 the dominant cover on the mountain slopes ; it apparently was more abundant at 

 lower levels, where it has been replaced by sage, before the extensive logging 

 operations late in the last century. In this region the Sierran forest includes three 

 major associations which replace one another with increasing elevation. The lower 

 zone is dominated by Jeffrey pine (Pinus jeffreyi) and white fir (Abies concolor). 

 Locally in protected canyons the common west-slope Sierran conifers, incense 

 cedar (Libocedrus decurrens), sugar pine (Pinus lambertiana) , and yellow pine 

 (Pinus ponderosa) , are also present. Common shrubs in the forest are green man- 

 zanita (Arctostaphylos patida), chinquipin (Castanopsis sempervirens) , deer 

 brush (Ceanotlius integerrimus) , white thorn (C. cordidatus) , and bitter cherry 

 (Prunus emarginata). Streamways support alder (Alnut tenuifolia) , serviceberry 

 (Amelanchier alnifolia), dogwood (Cornus calif ornica) , aspen (Populus tre- 

 midoides), black cottonwood (Popidus trichocarpa) , ehokecherry (Prunus de- 

 missa), rose (Rosa gymnocarpa) , and several species of willow (Salix spp.). The 

 middle forest zone, which assumes dominance near 7,500 feet, is characterized by 

 white fir (Abies concolor) and red fir (A. magnifica), with Jeffrey pine (Pinus 

 jeffreyi) frequent on rocky sites. Common shrubs in this cooler, moister area in- 

 clude pine-mat manzanita (Arctostaphylos nevadensis), chinquipin (Castanopsis 

 sempervirens), and huckleberry oak (Quercus vaccinif olia) . Dense thickets of 

 alder ( Ainu s tenuifolia) and bitter cherry (Prunus emarginata) choke the moister 

 swales and flats, associated with lodgepole pine (Pinus contorta) and aspen (Popu- 

 lus tremuloides) . The upper forest is a subalpine association, occurring chiefly 

 above 8,500 feet. Among its dominants are white-bark pine (Pinus albicaulis), 

 white pine (Pinus monticola) , and mountain hemlock (Tsuga mertensiana). The 

 higher mountain summits are largely barren to semibarren, and support an arctic- 

 alpine flora. 



Present climatic conditions at the Verdi locality may be judged from the weather 

 records at Reno, 8 miles east and 300 feet lower. From these data it is estimated 

 that annual rainfall at the locality is approximately 12 inches, falling largely in 

 the winter half of the year at which time it is accompanied by light snow. Average 

 annual temperature is approximately 48° P., with highest temperature about 

 102° P. and the lowest extreme -19° P. The average maximum July temperature 

 is estimated at 86° F. and the average January minimum temperature is near 



