Kay (1960) named the Masket Shale for a type section exposed northwest of Masket Peak, above March Spring in the northern Toquima Range. At the type section, the Masket lies above the Ordovician Antelope Valley Limestone (the Diana Formation which commonly forms the upper boundary is missing), and below the McMonnigal Limestone (Kay and Crawford, 1964).

Conodonts from the upper member of the formation are probably Early Devonian (McKee, 1976), while graptolites from the lower Bastille Member indicate a Silurian age (Kay and Crawford, 1964). The Masket Shale is correlative with the Roberts Mountains Formation and locally, as in the Petes Canyon area of the Toquima Range with the Roberts Mountains Formation plus the McMonnigal Limestone (McKee, 1976).

The Masket Shale is characteristically a buff-weathering, dark, laminated, argillaceous siltstone or limestone which Kay and Crawford (1964) divided into the lower Bastille Member and an upper unnamed member.

The Bastille Member consists of about 100 feet of light gray, medium to thick-bedded, faintly to strongly laminated dolomite overlain by about 25 feet of medium to thick-bedded limestone with abundant crinoids, brachiopods and corals (McKee, 1976b). These evenly laminated carbonates pass gradationally upward into an upper member about 400 feet in thickness which consists of various lithologies. The upper portion of this member is dominated by medium and thick-bedded, blocky weathering, platy limestones. The remainder is composed of both medium to thick-bedded limestones with graded lower beds and fine-grained laminated upper portions, and thin-bedded platy buff-weathering limestone which resembles the Roberts Mountains Formation (McKee, 1976b).

In the southern Toiyabe Range, between Pablo and Wall Canyons, Kay and Crawford (1964) have described about 500 feet of Masket Shale. It is composed dominantly of buff-weathering platy argillaceous to calcareous siltstone with some siliceous shale, and a few laminated dolomitic interbeds (Kleinhampl and Ziony, 1985). These rocks were originally mapped as Palmetto Formation by Ferguson and Cathcart (1954).

The Masket Shale is 450 to 500 feet thick in the northern Toquima Range (Kay and Crawford, 1964; McKee, 1976b), and about 500 feet in the Toiyabe Range (Kay and Crawford, 1964).

The Masket Shale has only been recognized within the northern Toquima and southern Toiyabe Ranges (Kay and Crawford, 1964).

The depositional setting for the Masket Shale is for all intents and purposes identical to the Roberts Mountains Formation. In general the Masket appears to have been deposited in local topographic depressions along the outer Devonian-Silurian shelf where both calcareous turbidites, in part derived from the Tor Limestone, and organic-rich anoxic muds were deposited (Matti and McKee, 1977). Water depths along the outer shelf were probably on the order of 100 to 250 meters (Matti and McKee, 1977; Mullens, 1980).