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Type Section Information

The Tuff of Hoodoo Canyon was named by McKee (1976b) for distinctive ash-flow tuffs along Hoodoo Canyon in T.13 N., R. 35 E., in the northern Toquima Range.

Geologic Age

The Tuff of Hoodoo Canyon is Oligocene in age. K-Ar biotite ages are 30.6 +/- 1.2 Ma (McKee, 1976b). The Needles Range Formation and biotite-rich tuff in the Simpson Park Mountains may correlate with the Tuff of Hoodoo Canyon (McKee, 1976b). The formation has a reverse remanent magnetic direction.

General Lithology

The Tuff of Hoodoo Canyon is a distinctive marker within the ash-flow tuff sequence in the Toquima Range, where it often forms numerous hoodoos of nonwelded dark gray biotite-quartz latite tuff (McKee, 1976b). The basal portion of the ash-flow sheet is soft, white, nonwelded tuff. The middle unit is densely welded, dark gray to black, devitrified tuff. It contains a discontinuous band of devitrified black glass near the base, and an upper soft and unwelded vapor-phase altered tuff. The unit commonly contains columnar jointing parallel to compaction layering. Large elongate cavities up to 3 inches long are parallel to the compaction foliation, as are abundant streamlined fiamme (flattened pumice), which accentuate the welded fabric of the rock.

About 25 percent of the rock is composed of phenocrysts of about 65 percent plagioclase, 15 percent biotite, 11 percent sanidine, 5 percent pyroxene, and minor amounts of chert and dacitic volcanic xenoliths. The groundmass is composed of devitrified shards (McKee, 1976b).

There is a major erosional unconformity between the Tuff of Hoodoo Canyon and the overlying Bates Mountains Tuff. The Hoodoo Canyon Tuff was completely eroded from parts of the area, and remains elsewhere as discontinuous pockets preserved beneath the Bates Mountains Tuff (McKee, 1976b). Its eruptive center is probably at or near the thickest sections preserved along the western flank of the northern Toquima Range.

Average Thickness

The Tuff of Hoodoo Canyon is 400 feet thick along Wildcat and Hoodoo Canyons on the west flank of the Toquima Range, and thins abruptly to about 100 feet in the central part of the range (McKee, 1976b).

Areal Distribution

The Tuff of Hoodoo Canyon is present in the Toquima Range and Simpson Park Mountains (McKee, 1976b).

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Last modified: 09/12/06