Pg. 9 (table 1), 11-14, pl. 1 (geol. map), pl. 3 (corr. chart), pl. 4 (fossil locs.). Shwin Formation. Formal proposal of name. Present in lower plate of Roberts thrust (carbonate eastern facies). Principally chloritic argillite, metadolerite, greenstone, chloritic phyllite, black limy slate, mottled shaly limestone, limy mudstone, and calc-phyllite. Locally formation is complexly even isoclinally folded, beds are commonly sheared out, and interlayering of metavolcanics and limy mudstone may indeed be wholly mechanical rather than depositional. Estimated thickness 1,500 to 2,000 feet. All contacts of formation with others are faults (with possible exception of one north of Hancock Canyon with dolomite correlated with El Dorado Dolomite, and even this is sheared). Age is considered Middle Cambrian, based on fossils (trilobites, brachiopods). Report includes geologic map, faunal list, correlation chart.
Well exposed on and east of Shwin Ranch, from which formation is named, on south slope of the ridge between Goat Canyon and the North Fork of Mill Creek, northern Shoshone Range, Mount Lewis 15-min quadrangle, Lander Co., northern NV.

Source: Publication; US geologic names lexicon (USGS Bull. 1350, p. 692).