stripes
The type locality for the peralkaline Idaho Canyon tuff lies on the southern and southeastern sides of Big Mountain, but it outcrops extensively over northern Washow and western Humboldt Counties and extends northwards into Oregon. Thicknesses of the tuff increase towards the Virgin Valley, which lies approximately in the centre of the distribution, and the source is probably in this area but has not been identified. At most localities the rock is densely welded and granophyrically crystallized throughout its vertical extent. It contains phenocrysts of sodium-rich sanidine and quartz and in the groundmass sodic amphibole and pyroxene; arfvedsonite is found in gas cavities. The rock is comenditic.
NOBLE, D.C., MCKEE, E.H., SMITH, J.G. and KORRINGA, M.K. 1970. Stratigraphy and geochronology of Miocene volcanic rocks in northwestern Nevada. Professional Paper, United States Geological Survey, 700-D: 23-32