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TUFF OF CLIPPER GAP

Type Section Information

The Tuff of Clipper Gap was designated by Gromme and others (1972) for tuffs originally mapped as Bates Mountains Tuff. The tuff is the youngest unit exposed in the Toquima, Monitor, and northern Hot Creek Ranges. The type section is in the northern portion of the Toquima Range at the top of ridge north of Clipper Gap Canyon in T.16 N., R.46 E.

Geologic Age

The Tuff of Clipper Gap lies on the Bates Mountain Tuff and is early Miocene in age. K-Ar dating in Clipper Gap Canyon yields an age of 22.2 Ma, while a sample from near Eureka gives an age of 22.1 +/- 0.7 Ma (McKee, 1976b; Gromme and others, 1972).

General Lithology

The Tuff of Clipper Gap is very similar lithologically with the upper cooling unit, minus the "swiss cheese" lithology of the underlying Bates Mountain Tuff. It is a pink to light red, crystal-poor rhyolite tuff containing about 5 percent phenocrysts which are dominantly sanadine, with lesser amounts of quartz, plagioclase and biotite. As exposed in Clipper Gap Canyon in the northern Toquima Range, it consists of a basal nonwelded zone that becomes progressively more densely welded upward. Typically the tuff has strongly developed eutaxitic fabric, which locally resembles flow banding, and a thin black vitrophere is present at the base of the densely welded tuff (McKee, 1976b).

Directions of remanent magnetization are unique in the tuff. They are nearly horizontal with inclinations ranging from 8.3 to - 8.1 degrees, and an average declination of 158 degrees (Gromme and others, 1972). This direction separates the Tuff of Clipper Gap from all other ash-flow tuff sheets in the region.

Average Thickness

The Tuff of Clipper Gap is 70 to 100 feet thick in the northern Toquima Range (McKee, 1976b). Gromme and others (1972) estimated the average thickness of the Clipper Gap to be about 90 feet.

Areal Distribution

The Tuff of Clipper Gap is exposed within the Toquima, Monitor and northern Hot Creek Ranges (Gromme and others, 1972). The maximum lateral extent of the Tuff of Clipper Gap is 185 km with an area of approximately 190 cubic kilometers (Gromme and others, 1972).


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