The Tuff of Lunar Cuesta was named for exposures on and near Lunar Cuesta in T. 6 and 7 N., R. 52 E., in the Lunar Crater Quadrangle in the southern Pancake Range (Snyder and others, 1972).

The Tuff of Lunar Cuesta is Miocene in age. K-Ar ages of 25.5 +/- 0.8 Ma on biotite, and 22.5 +/- 0.8 Ma on sanadine have been reported by Ekren and others (1973). In the Pancake Range, the Tuff of Lunar Cuesta locally overlies the Shingle Pass Tuff or the Tuff of Stuben Knob, and is overlain by the Tuff of Buckwheat Rim or Tuff of Buckskin Point (Snyder and others, 1972; Ekren and others, 1972; Ekren and others, 1973).

The Tuff of Lunar Cuesta is a simple, magnetically reversed, cooling unit of blue-gray, light brown weathering, vitric to mostly devitrified, quartz latite ash-flow tuff with about 20 to 35 percent phenocrysts. Phenocrysts are about 45 to 75 percent potassium feldspar, 15 to 20 percent quartz, 10 to 15 percent biotite, 7 to 15 percent alkali feldspar, 3 percent hornblende and 1 percent opaques (Snyder and others, 1972). The tuff contains abundant lithic fragments of the underlying Shingle Pass Tuff in the basal portion of the unit (Ekren and others, 1972).

The Tuff of Lunar Cuesta is as much as 400 feet thick in the southern Pancake Range.

The Tuff of Lunar Cuesta forms a large portion of the southern Pancake Range but is not recognized elsewhere in the evaluation area.