Pg. 17-18, 36 (table 1), pI. 1. Aura Formation. Upper portion composed of thin-bedded brown to black phyllite and chert alternating with thick blue-gray limestone layers; middle member of 500 feet of buff medium-grained quartzite often missing; lower part similar to upper member with fewer and thinner limestone layers. Thickness about 3,800 feet, uncertain because of faulting and intrusive igneous stocks. Overlies Porter Peak Limestone (new); underlies Chellis Limestone (new), both contacts conformable. Age is tentatively Ordovician, based on regional correlation.
Named from Aura (Columbia) mining district on east slope Bull Run Mountains, [Bull Run 15-min quadrangle], Elko Co., northeastern NV. Formation exposed in undulating band trending east-west across Bull Run Mountains south of Blue Jacket Peak; continuity disrupted by intrusion of White Rock stock and by faulting which offsets part of formation.

Source: US geologic names lexicon (USGS Bull. 1350, p. 36).