Axelrod: The Pliocene Verdi Flora of Western Nevada 99 



the Mehrten, the bulk of which represents agglomerates and tuffs, as well as mud- 

 flow breccias, conglomerates, and coarse tuffaceous sandstones deposited by- 

 streams. Since they represent different environments — one largely fluvio-lacus- 

 trine, the other chiefly volcanic and fluvatile — it seems best to give them separate 

 names. In connection with their close lithic relationship, it is pertinent that the 

 formations are largely of the same age. The occurrence of Nannippus tehonensis in 

 the basal beds at Coal Valley dates its lowest part as Early Clarendonian (Stirton, 

 1939, p. 635; Axelrod, 1956, p. 33). The Mehrten formation on the west slope of 

 the Sierra Nevada has Early Clarendonian faunas at Two-Mile Bar (Stirton and 

 Goeriz, 1942), Goodwin Dam (Stirton and Goeriz, 1942), and Springfield Shaft 

 (Merriam and Stock, 1933) ; all of them are at the base of the formation. The Table 

 Mountain, 1944&) and Remington Hill (Condit, 1944a) floras of Early Claren- 

 donian age also have a similar stratigraphic position in the formation on the west 

 Sierran slope. The higher sections of the Coal Valley formation range into the 

 Hemphillian, as judged from the Yerington fauna (Stirton, 1939, p. 637), which 

 is in the Morgan Ranch formation just above the top of the Coal Valley formation 

 (Axelrod, 1956, p. 67) , and from the age indications of the Verdi flora as discussed 

 below. The upper parts of the Mehrten formation to the west also are Hemphillian, 

 as shown by the Oakdale flora (Axelrod, 1944b) and fauna (Stirton and Goeriz, 

 1942). 



Eastward, the Coal Valley interfingers with the Truckee formation. At many 

 points along the west margin of the Carson Sink the Truckee contains thin sand- 

 stones and pebble beds derived from erosion of the Kate Peak andesite. Further- 

 more, old centers of Kate Peak eruption occur in several areas at the west margin 

 of the Carson Sink. In the hills south of Fernley relatively complete sections of the 

 Coal Valley and Truckee formations are interfingered. It is here that Kate Peak 

 andesite rests on rhyolite tuff that appears to be equivalent to the Valley Springs 

 formation which underlies the Mehrten formation on the west Sierran slope, and 

 grades upward into the fluvio-lacustrine Coal Valley formation as characterized 

 by andesitic pebble beds and sandstones. Thin basalt tuffs occur locally in this sec- 

 tion, and increase rapidly both in frequence and in thickness a few miles eastward 

 as the Coal Valley thins to a few pebbly sandstones and sandy shales in a typical 

 Truckee section. It is apparent that the Truckee basin, which coincided largely 

 with the present area of the Carson Sink, was being filled in part by streams carry- 

 ing typical Kate Peak andesitic debris eastward from Sierran and other nearby 

 centers of eruption. 



Lithology 



In the Verdi area, the Coal Valley formation commonly rests on an old soil that 

 developed on volcanics or on basement rocks. The soft, uncompacted regolith ranges 

 from 2 to 3 feet up to 8 or 10 feet thick in some areas. It is typically dark brown 

 to chocolate, or locally black in color, and grades down into the underlying rocks. 

 In some ways it resembles a dark prairie soil, but was not studied in detail. 



For mapping purposes the overlying section was divided into two sedimentary 

 members, separated generally by a basalt of discontinuous outcrop occurrence. 

 Although the sedimentary units differ lithologically in their major features, similar 



