The Windmill was named by Johnson (1965) for laminated and bioclastic limestones at Coal Canyon in the northern Simpson Park Mountains.

The Windmill Limestone is considered Lower Devonian (Lochkovian) in age (Johnson, 1965). Lithologically the Windmill is very similar to the McMonnigal Limestone exposed 42 kilometers west-southwest at Ikes Canyon in the Toquima Range (Kay and Crawford, 1964). They may in fact be lithostratigraphic equivalents (Matti and others, 1975) although McKee and others (1972) have suggested a correlation with the Rabbit Hill Limestone.

The Windmill Limestone is characterized by very fine-grained, laminated and thinly bedded, lime mudstone and wackestone, and thick bedded (up to 1 meter) allodapic limestone which are compositionally similar to, and more abundant than, those in the Roberts Mountains Formation which it conformably overlies.

In the Dobbin Summit area of the Monitor Range, the Windmill Limestone is composed of laminated, thin-bedded, silty, yellow-gray to pinkish lime mudstones, and 12 to 30 inch thick beds of graded and nongraded, medium to dark gray or pinkish weathering limestone (Wise, 1977). The coarsely graded beds contain well-rounded mudstone and wackestone interclasts as well as corals and crinoids. The nongraded packstones are composed of about 40 percent micrite and 55 percent fossil fragments, pellets and organic material, and about 5 percent quartz sand and silt.

The Windmill Limestone is 350 to 455 feet thick at Copenhagen and about 550 feet thick at Coal Canyons in the Simpson Park Mountains (Matti and others, 1975; Johnson and Murphy, 1969), about 165 feet at Dobbin Summit in the Monitor Range (Wise, 1977), and 900 feet at Wenban Peak in the Cortez Mountains (Slatten, 1978).

The Windmill Limestone has been recognized within the Cortez and Simpson Park Mountains, Monitor and Sulphur Spring Ranges.

The Windmill Limestone represents low-energy subtidal basinal deposition along the outer shelf and upper slope, oceanward of the Devonian platform margin. Silty, laminated and massive, burrowed dolomite and lime mudstones probably represent suspended deposition in local depressions along the outer shelf. Allodapic, thick-bedded sheets of graded and nongraded skeletal packstone and grainstones probably represent debris flows derived from time-equivalent shoal water bank deposits of the Lone Mountain Dolomite as it began to prograde basinward during Lochkovian time (Johnson and Murphy, 1969; Matti and others, 1974; Slatten, 1978).