The Tuff of White Blotch Spring was named by Ekren and others (1971) for exposures in the Nellis Bombing and Gunnery Range.

The Tuff of White Blotch Spring is Miocene in age and gives radiometric ages ranging from 21 to 25 Ma with an average of about 23 Ma (Kleinhampl and Ziony, 1985).

The Tuff of White Blotch Spring is commonly a rhyolitic tuff composed of two brown to reddish, densely welded cooling units on the order of 400 to 500 feet thick. In the Reveille Range, three cooling units are present and the tuff is about 2,000 feet thick (Ekren and others, 1971). Phenocryst content varies in various ranges but is commonly about 30 to 35 percent of the rhyolite. Typically 35 to 40 percent of the phenocrysts are quartz, 30 to 35 percent alkali feldspar, 25 to 30 percent plagioclase and up to 5 percent biotite (Ekren and others, 1971). Lithic fragments as well as pumice lapilli and blocks are locally present in some exposures of the tuff.

On average the White Blotch Spring is about 800 to 900 feet thick. It is about 2,000 feet thick in the Reveille Range (Ekren and others, 1971).

The Tuff of White Blotch Spring is widely distributed in southern Nye County in the Nellis Bombing Range area, and is present in the Reveille and Kawich Ranges within the present evaluation area.