The Dead Horse Tuff is named for Dead Horse Creek in Copper Basin, in T. 45 N., R. 58 E. in the southwestern corner of the Jarbidge Quadrangle (Coats, 1964).

The Dead Horse Tuff is considered Late Eocene in age with a K-Ar biotite age of 39.9 Ma (Coats, 1974). It is one of the few Eocene ignimbrites in the evaluation area, concentrated in the northern portion of Elko County.

The Dead Horse Tuff is a crystal-vitric and pumiceous gray, white, chocolate brown, or green, quartz latite to biotite rhyolite tuff. Much of the unit is massive devitrified welded tuff. The latitic tuff has phenocrysts of plagioclase, hypersthene and biotite while the rhyolitic members have abundant quartz, sanidine, biotite and plagioclase.

The Dead Horse Tuff is about 5,200 feet thick along the western flank of the Jarbidge Mountains in the Jarbidge Quadrangle (Coats, 1964).

The Dead Horse Tuff is exposed in the Jarbidge Mountains.