THE PLIOCENE VERDI FLORA OF 

 WESTERN NEVADA 



BY 



DANIEL I. AXELPOD 



ABSTRACT 



The Verdi flora of nineteen species is preserved in andesitic sandstones of the Coal Valley for- 

 mation near Verdi, Nevada. The formation rests unconformably on Mio-Pliocene Kate Peak 

 andesite on the south side of the basin, but on the north it lies on Oligoeene Alta andesite or 

 Jurassic granodiorite, the Kate Peak having been eroded there owing to uplift of the Peavine 

 block by faulting following vulcanism. The Coal Valley rocks, which accumulated in a basin 

 formed by downwarping and faulting, comprise (1) a lower, dark-colored, coarse conglomerate- 

 breccia-sandstone member, (2) an olivine basalt, and (3) an upper, light-colored, sandstone- 

 pebble conglomerate-shale-diatomite member. The flora comes from near the middle of the upper 

 member, and fragmentary mammalian fossils lie several hundred feet above and below it. 



The plants are preserved in sediments that were deposited in the central floodplain area at an 

 altitude of approximately 2,500 feet, and in a region of comparatively low relief. The flora 

 resembles modern vegetation at the lower margin of yellow pine forest on the west slope of the 

 Sierra Nevada and in southern California. Cottonwood and willow dominated the stream- and 

 lake-borders on the Verdi floodplain. Nearby exposed slopes and well-drained flats supported an 

 oak woodland and savanna, with chaparral present locally. A forest of pine and fir, with asso- 

 ciates of manzanita, cherry, poplar, aspen, and willow lived chiefly in the bordering hills, extend- 

 ing locally into the lowlands on stream banks. 



Verdi climate was subhumid, with yearly rainfall ranging from 18 to 20 inches in the lowlands, 

 and increasing to 25 inches at the forest margin. Precipitation was distributed as winter rains 

 and summer showers in contrast to the present winter rain and snow. Average January tempera- 

 ture was at least 10° F. higher, and the frost-free season was fully two months longer than that 

 at Verdi today. 



The Middle Pliocene (Hemphillian) age of the flora is indicated by its geographic, climatic, 

 and cliseral relations, a conclusion in harmony with the age implications of associated mam- 

 malian fossils. 



INTRODUCTION 



Sediments interbedded with the Tertiary volcanics in the central to northern part 

 of the Sierra Nevada have yielded a number of fossil floras, distributed from near 

 sea level in the western piedmont area to the summit of the range. From detailed 

 paleoecological studies of these floras it has been possible to reconstruct the vegeta- 

 tion, climate, and topography of the region during much of the period. The evi- 

 dence shows that lowland subtropical forests covered the range in the Early 

 Tertiary, that mixed deciduous temperate forests dominated the low range in the 

 middle of the period, and that semiarid woodland occupied the flanks of the range 

 and temperate forest the upper slopes of the lower barrier during the Late 

 Tertiary. The pronounced zones of vegetation and climate that characterize the 

 range today developed only at the close of the Cenozoic, at which time the massif 

 was elevated to its present heights by warping and faulting (Axelrod, 1957a). 



Parts of the Tertiary Sierran section also occur to the east of the range in Cali- 

 fornia and Nevada. Although fossil floras have been recovered from these rocks at 

 several localities, they have not been analyzed up to the present time. Of these, the 

 Pliocene Verdi and Chalk Hills floras, situated 8 miles west and 15 miles southeast. 



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