102 University of California Publications in Geological Sciences 



floodplain probably transported the relatively homogeneously colored sandy sedi- 

 ments into the lowlands. The beds show rapid lateral and vertical variation in tex- 

 ture, and are typified by sedimentary structures such as scour-and-fill, cross- 

 bedding, graded bedding, lenticularity, and numerous small discontinuities, all of 

 which are regularly developed under conditions of flood deposition. The sediments 

 are chiefly coarse and gritty, and poorly indurated. They are associated with soft, 

 pebbly sandstones and pebble conglomerates, ranging from gray or brown to 

 yellow-brown in color. In thickness they vary from a few inches up to beds 8 to 10 

 feet thick. Regularly associated with the sandstones and conglomerates are soft, 

 regolithic-like sediments that may well represent old soils that developed on the 

 floodplain. Gray to brown tuffaceous shales, and creamy to white diatomaceous 

 beds are conspicuous in the section. 



South of the river, in the area near Fleish and eastward for over a mile, the 

 lowest exposed beds represent a light-gray to tan section of coarse to fine sand- 

 stone, pebble conglomerate, and thin diatomite. A few thin andesite tuffs are repre- 

 sented in the section. Blue to blue-gray andesitic sandstones are prominent in the 

 area, ranging from a few feet up to 10 or 15 feet thick, and they are regularly 

 current marked. To the east this section overlies the prominent dark-colored con- 

 glomerate of the lower member. The gradational contact is generally marked by 

 the disappearance of coarse conglomerate, and a change in color from dark gray 

 and dark brown to light gray, tan, and locally white. The white beds are lenses of 

 diatomite which are common in the section. Although they are comparatively 

 abundant, they are generally thin, ranging from a few inches to a few feet thick, 

 and commonly lenticular. 



The higher parts of the Coal Valley formation are typified by light-colored, 

 fluvio-lacustrine sediments in which diatomite is prominent. Within the mapped 

 area diatomite ranges up to 30 or 40 feet thick or more, associated regularly with 

 poorly indurated gray to blue-gray andesitic sandstones and pebble beds. To the 

 east, outside the limits of the area, diatomite makes up an even more prominent 

 part of the section. At Chalk Bluffs, on the north side of the Truckee River just 

 east of Lawton, it is fully 500 feet thick and extends to the north and south where 

 it overlaps the older volcanics on the front Peavine Mountain and the Carson 

 Range. Apparently the same section occurs also at the base of Crystal Peak ridge 

 west of Verdi, in California. 



Locally the diatomaceous beds are tuffaceous, and north of Mogul they are 

 associated with rhyolite tuff. The center of eruption of this tuff may have been in 

 the area to eastward, for in the lower drainage of Long Valley Creek in the north- 

 ern part of the Virginia City Quadrangle 15 miles east, there are rhyolite centers 

 which contributed pumiceous tuffs to the upper part of the formation there 

 (Thompson, 1956, p. 56). 



The elastics associated with the higher parts of the upper member include 

 poorly indurated, blue to blue-gray, coarse- to fine-grained sandstone and sandy 

 shales. Locally, however, there are interbeds of yellowish-brown or orange sand- 

 stones derived from the altered volcanic sections that border the basin. In general, 

 the elastics occur in beds ranging from a few inches to several feet thick. Like the 

 rest of the section, they regularly show numerous cross-beds and other current 



